Defect detection system based on zone plate array imaging

Abstract

The invention provides a defect detection system based on zone plate array imaging. The defect detection system comprises a light source, a zone plate array and an image acquisition component, wherein the wave zone plate array is formed by arranging a plurality of wave zone plate units, and imaging areas of different wave zone plate units are separated from one another; multiple beams of light emitted by the light source pass through an object to be measured and then enter each zone plate unit on the zone plate array to form a convergent light field, and the convergent light field corresponding to each zone plate unit is transmitted to the image acquisition component to be received and imaged. Compared with the prior art, the zone plate array is adopted for imaging, the field of view of the object space is effectively increased while high-resolution imaging precision is obtained, the defect detection yield can be greatly improved, and therefore the requirement of the industry for the defect detection yield is met.

Description

Technical Field

[0001] The present disclosure relates to the field of lithography technology, and particularly to a defect detection system based on zone plate array imaging. Background Art

[0002] As the integrated circuit technology node develops towards below 28 nm, defect contamination detection plays an increasingly important role in the chip production process. With the reduction of the design size, the chip manufacturing process becomes more cumbersome and complex, and the possibility of defects and contamination in the manufacturing process is higher. Especially when a new generation of chips is just launched and the new manufacturing process is not yet mature, it is very easy to cause the functional failure of the integrated circuit. In addition, as the technology node becomes smaller, small-size defects and particulate contaminants that do not affect the original technology node will have a key impact on the new technology node, making defect contamination detection equipment crucial for chip production. If an error occurs in the chip during any manufacturing step, the finally completed chip must be defective. All the manufacturing processes after the error-making step are not only useless but also cause a large amount of waste of time and money. The ideal detection technology should run through all links of chip manufacturing and be discovered and reported during the manufacturing process of the error-making link of the chip, and the defective wafer should be removed from the production line for repair and remanufacture. By using detection equipment, chip manufacturers can effectively improve the yield rate, save costs and increase benefits.

[0003] In addition, as the template of the lithography process, whether there are defects on the mask directly determines the yield rate of the lithography process. Once there are defects on the mask that can be replicated by lithography, these defects will be repeatedly transferred to the wafer, resulting in the failure of all wafers prepared with this defective mask as the template, which will inevitably cause huge economic losses to chip manufacturers. Especially at the 7 nm and below technology nodes, extreme ultraviolet lithography is the most promising technical means. In the semiconductor manufacturing process, extreme ultraviolet mask technology is considered to be one of the most critical technologies for the successful implementation and development of extreme ultraviolet lithography technology. Different from traditional lithography masks, EUV masks adopt a multi-layer film structure. The preparation process of extreme ultraviolet masks is very complex, and each process step will inevitably introduce defects, and the lithography-defectible defects on the extreme ultraviolet masks directly affect the yield rate of the lithography process and must be strictly controlled.

[0004] Therefore, whether it is for the preparation of masks or the production of wafers, it is necessary to detect the possible defects on them throughout the process. Once the existence of defects is found, the defective mask or wafer should be removed from the production line to avoid unnecessary economic losses to the lithography process.

[0005] With the development of lithography technology, mask and wafer defect detection technologies have received increasing attention from domestic and foreign research institutions. Subsequently, numerous production enterprises of mask and wafer defect detection equipment have emerged. Currently, the lens imaging technology is adopted for both mass-produced mask and non-patterned wafer detection equipment. Whether it is for DUV (deep ultraviolet light) or EUV (extreme ultraviolet light) mask and wafer defect detection, the pursuit is wavelength detection technology. Therefore, the wavelengths of the detection light sources used are generally 266nm, 257nm, 213nm, 193nm, and 13.5nm. The shorter the wavelength, the higher the requirements for the material and processing quality of optical components. Therefore, it is very difficult to fabricate a lens imaging system suitable for the DUV band, especially the EUV band, with high NA (numerical aperture), large field of view, and low aberration. At the same time, the cost is very high. Using a lens system for imaging requires extremely high alignment accuracy of the optical system, which is extremely difficult to align. The auxiliary alignment equipment required is also extremely expensive. If the alignment does not meet the requirements, the resolution of the imaging system will be severely affected.

[0006] In recent years, with the continuous development of micro-nano processing technology, an imaging technology based on Fresnel zone plates has received increasing attention. A Fresnel zone plate generally consists of a series of transparent and opaque concentric rings. It can form a real image of a point light source. Therefore, it can be considered that its function is equivalent to that of a converging lens and can be used as an imaging device. If used as an imaging device, resolution is an important indicator. The width of the outermost ring of the zone plate determines its resolution. Due to the continuous progress of manufacturing processes, the width of the outermost ring of the zone plate has been able to reach the order of dozens of nm. Therefore, the imaging resolution of the zone plate has developed by leaps and bounds. Currently, a defect resolution of dozens of nm can be achieved. Moreover, the preparation of the zone plate is of low difficulty and low cost. Applicable zone plates can be prepared according to different illumination wavelengths and imaging resolutions. Therefore, the applicable range of illumination wavelengths is very wide. However, although the zone plate imaging can obtain extremely high resolution, its size is very small, only on the order of millimeters or even with a diameter of only a few hundred micrometers. This results in a very small object space field of view during imaging, usually only dozens to hundreds of micrometers. Such a small field of view determines that its efficiency for mask or wafer defect detection is very low and cannot meet the industrial demand for mass production. Therefore, the zone plate imaging technology is currently only applicable to the scientific research field.

[0007] Therefore, currently, the problems of difficult processing, high cost, and difficult alignment of the lens system of lens imaging defect detection equipment, as well as the small field of view of zone plate imaging defect detection equipment, which cannot meet the industrial mass production demand, are technical problems that urgently need to be solved in this field. Summary of the Invention

[0008] The purpose of the present disclosure is to provide a defect detection system based on zone plate array imaging.

[0009] An embodiment of the present disclosure provides a defect detection system based on zone plate array imaging, including:

[0010] A light source, a zone plate array, and an image acquisition component; wherein, the zone plate array is formed by arranging a plurality of zone plate units, and the imaging regions of different zone plate units are separated from each other;

[0011] Multiple beams of light emitted by the light source pass through the object to be measured and then enter each zone plate unit on the zone plate array respectively to form a converging light field, and the converging light field corresponding to each zone plate unit propagates to the image acquisition component and is received and imaged.

[0012] In some embodiments of the present application, the system further includes a cavity, the light source is hermetically connected to the cavity, and the zone plate array and the image acquisition component are arranged in the cavity.

[0013] In some embodiments of the present application, the cavity is a vacuum cavity.

[0014] In some embodiments of the present application, the system further includes a vibration isolation table, and the vacuum cavity is arranged on the vibration isolation table.

[0015] In some embodiments of the present application, the vibration isolation table provides 90% vibration isolation at 2 Hz.

[0016] In some embodiments of the present application, high-purity nitrogen is introduced into the cavity for gas bath protection.

[0017] In some embodiments of the present application, the target area of the image acquisition component is greater than or equal to the imaging area of the zone plate array.

[0018] In some embodiments of the present application, the image acquisition component includes at least one CCD camera.

[0019] The advantages of the present disclosure compared with the prior art are as follows:

[0020] The defect detection system based on zone plate array imaging provided by the present disclosure includes: a light source, a zone plate array, and an image acquisition component; wherein, the zone plate array is formed by arranging a plurality of zone plate units, and the imaging regions of different zone plate units are separated from each other; multiple beams of light emitted by the light source pass through the object to be measured and then enter each zone plate unit on the zone plate array respectively to form a converging light field, and the converging light field corresponding to each zone plate unit propagates to the image acquisition component and is received and imaged. Compared with the prior art, the present application uses a zone plate array for imaging, while obtaining high-resolution imaging accuracy, effectively increasing the field of view of the object space, and can greatly improve the defect detection yield, so as to meet the requirements of the industrial community for the defect detection yield. Description of the Drawings

[0021] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present disclosure. Moreover, throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0022] Figure 1 The schematic diagram of the principle of zone plate imaging is shown;

[0023] Figure 2 The schematic structural diagram of a defect detection system based on zone plate array imaging provided by the present disclosure is shown;

[0024] Figure 3 The schematic structural diagram of the zone plate array provided by the present disclosure is shown;

[0025] Figure 4 The schematic diagram of the principle of zone plate array imaging provided by the present disclosure is shown. Detailed Embodiments

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present disclosure. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0027] Schematic structural diagrams according to embodiments of the present disclosure are shown in the drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0028] In the context of the present disclosure, when a layer / component is referred to as being "on" another layer / component, the layer / component can be directly on the other layer / component, or there can be an intermediate layer / component between them. Additionally, if a layer / component is "on" another layer / component in one orientation, then when the orientation is reversed, the layer / component can be "under" the other layer / component.

[0029] Currently, the lens system of the lens imaging defect detection device has problems such as high processing difficulty, high cost, and difficult alignment, and the field of view of the zone plate imaging defect detection device is small, which cannot meet the mass production requirements of the industry.

[0030] To solve the problems existing in the prior art, an embodiment of the present disclosure provides a defect detection system based on zone plate array imaging. While obtaining high-resolution imaging accuracy, this system effectively increases the field of view on the object side, can greatly improve the defect detection throughput, and thus meet the industrial demand for defect detection throughput. Through the design of zone plate arrays with different parameters, this system can be applicable to various illumination wavelengths, can meet the wavelength detection requirements in the DUV and EUV bands, is applicable to the defect detection requirements of masks, wafers, etc., and can also be applicable to the high-resolution imaging requirements in the fields of life science, materials science, surface science, etc. The following will be described in conjunction with the accompanying drawings.

[0031] Fresnel zone plates are often used as imaging lenses in high-resolution microscopy imaging technology. The principle of zone plate microscopy imaging is as Figure 1 shown. The illumination light source irradiates the object to be measured. When passing through the object to be measured, it will carry the defect information on the object. The transmitted light after passing through the object to be measured carrying the defect information irradiates onto the zone plate. The zone plate acts as an imaging element and functions as an imaging lens, magnifies the illumination light irradiated onto the zone plate, and is finally received by the CCD camera. CCD is the abbreviation of charge coupled device.

[0032] For opaque objects, the zone plate imaging principle is the same, except that the illumination light is changed from transmissive to reflective. The reflected light of the object carries the defect information and irradiates onto the zone plate, and is received by the CCD camera after imaging. By designing the parameters of the zone plate and appropriately adjusting the object distance and image distance of the zone plate, the magnification required for imaging can be obtained. Through the magnifying imaging of the zone plate, the tiny defect information on the object will be effectively magnified to a size that can be detected by the CCD camera, and thus captured by the CCD camera. Through the processing of the later defect extraction algorithm, information such as the size, type, and position of the defect can be obtained. This is the basic principle of mask and wafer defect detection.

[0033] The resolution of zone plate imaging is determined by the width of its outermost ring. With the increasing progress of micro-nano processing technology, the zone plate fabrication technology is becoming more and more mature, and the width of the outermost ring can be made to be dozens of nm. Therefore, the zone plate can obtain an imaging ability with ultra-high resolution of dozens of nm. However, the diameter of the zone plate is very small, usually in the order of mm or even hundreds of um, which directly leads to a very small field of view on the object side of zone plate imaging. Although its resolution is very high, it is not suitable for the mass production requirements in fields such as defect detection.

[0034] In order to make full use of the extremely high-resolution imaging ability of the zone plate and improve the detection throughput to meet the mass production requirements of the industry, this application proposes a defect detection system based on zone plate array imaging, as Figure 2As shown, the system includes: a light source 100, a zone plate array 200, and an image acquisition component 300; wherein, the zone plate array 200 is formed by arranging a plurality of zone plate units 210, and the imaging regions of different zone plate units 210 are separated from each other. Specifically, the zone plate array 200 is to fabricate periodically distributed zone plate units 210 on a substrate 220, such as Figure 3 shown.

[0035] The light source 100 can be a DUV light source or an EUV light source. The light source 100 can be composed of multiple light sources, and each light source emits a beam of illumination light, so as to obtain multiple beams of illumination light. Or the illumination light emitted by the light source 100 can be split into multiple beams of illumination light by a beam splitter.

[0036] The target surface area of the image acquisition component 300 is greater than or equal to the imaging area of the zone plate array. The image acquisition component 300 can include at least one CCD camera, that is to say, the image acquisition component 300 can be composed of one CCD camera according to actual needs. When the target surface area of one CCD camera cannot meet the requirements, it can also be composed of multiple CCD cameras.

[0037] The multiple beams of illumination light emitted by the light source 100 pass through the object to be measured and then enter each zone plate unit 210 on the zone plate array 200 to form a converging light field. The converging light field corresponding to each zone plate unit 210 propagates to the image acquisition component 300 and is received and imaged. In fact, it is the same as the imaging principle of the single zone plate Figure 1 shown, only multi-zone plate integration is adopted and imaging is performed simultaneously to improve the productivity of the imaging system.

[0038] Each zone plate unit 210 is equivalent to an imaging lens. Although the imaging field of view of each zone plate unit 210 is very small, the form of the zone plate array can increase the total object space field of view of the imaging system by several times or even dozens of times. Therefore, the efficiency of the imaging system can be greatly improved. The number of zone plate units 210 in the zone plate array 200 determines the total imaging field of view of the final system. The optimal number of zone plate units can be designed according to the productivity requirements of different application scenarios.

[0039] Although the larger the number of zone plate units 210, the larger the field of view, it is also necessary to comprehensively consider the image space field of view. Since each zone plate unit 210 needs to image the object space field of view onto the CCD camera, in order to prevent the images formed by different zone plate units 210 from interfering with each other, the spacing between the zone plate units 210 needs to be optimally designed according to the magnification required by the system. The larger the magnification of the system, the larger the spacing between the zone plate units 210, and then the area corresponding to the final image space field of view will also become very large. If the area of the image space field of view exceeds the target area of a CCD camera, then multiple CCD cameras need to be configured according to the actual situation to ensure that the imaging images of all zone plate units 210 can be obtained simultaneously. Theoretically, if the image space field of view, i.e., the total field of view of the CCD camera, is large enough, then the number of zone plate units 210 in the zone plate array can be sufficient.

[0040] Taking a zone plate array with 4 zone plate units 210 as an example, the imaging principle is as Figure 4 shown. Actually, it is the same as the imaging principle of a single zone plate Figure 1 shown, except that multiple zone plate units 210 are integrated and imaged simultaneously to improve the productivity of the imaging system. This design only needs to reasonably design the spacing between the zone plate units 210 according to the magnification required by the system to ensure that the imaging areas of each zone plate unit 210 in the image space field of view are separated from each other and do not interfere with each other. When the imaging areas of 4 zone plates are within the target area of a CCD camera, the imaging images of 4 zone plate units 210 can be obtained simultaneously. When the number of zone plate units 210 is too large and the imaging area exceeds the area of a CCD target, the number of CCD cameras can be reasonably increased to meet the requirements of the imaging image space field of view area.

[0041] Figure 4 The principle of transmissive imaging is shown, that is, the illumination light can penetrate the object to be measured, carry information such as the defects of the object, and be received and magnified by the zone plate unit 210 and imaged onto the CCD camera, so that information such as the minute defects on the object to be measured can be imaged. This system is also applicable to reflective imaging. At this time, the illumination light irradiates the object to be measured and is reflected. The reflected light carries information such as the defects of the object to be measured, and is received and magnified by the zone plate unit 210 and imaged onto the CCD camera, so that information such as the minute defects on the object to be measured can be imaged.

[0042] In some embodiments of the present application, the defect detection system based on zone plate array imaging provided by the present application may further include a cavity (not shown in the figure). The light source 100 is hermetically connected to the cavity, and the zone plate array 200 and the image acquisition component 300 are arranged in the cavity.

[0043] For the illumination light in the DUV band, high-purity nitrogen can be introduced into the cavity for gas bath protection. Specifically, the illumination light applicable to this system has a wide wavelength range. For the illumination light in the DUV band, air has a strong absorption of the illumination light. Therefore, the imaging system needs to be placed in a sealed cavity and high-purity nitrogen is introduced for gas bath protection.

[0044] For extreme ultraviolet illumination light, the cavity is a vacuum cavity. Light with an extreme ultraviolet wavelength must be used in a vacuum environment, otherwise it will be quickly absorbed by air. Therefore, the imaging system requires a vacuum cavity to provide a vacuum environment, and the generally required vacuum degree is better than 10 -6 hPa.

[0045] The defect detection system based on zone plate array imaging provided by this application has very strict requirements on the vibration of the system. Especially for high-resolution defect detection in the extreme ultraviolet band imaging, the relative vibration displacement between the object to be measured and the zone plate cannot exceed 5 nm. Therefore, vibration isolation needs to be carried out on the entire device, and the entire device needs to be installed on a vibration isolation table. Therefore, this system also includes a vibration isolation table (not shown in the figure), and the vacuum cavity is arranged on the vibration isolation table. The vibration isolation table provides 90% vibration isolation at 2 Hz.

[0046] The advantages of this disclosure compared with the prior art are as follows:

[0047] The defect detection system based on zone plate array imaging provided by this disclosure uses a zone plate array for imaging. The preparation of the zone plate is of low difficulty and low cost, and the optical path alignment is simple, which solves the problems of high manufacturing cost, large manufacturing difficulty, and complex optical path alignment in the lens imaging-based defect detection system. The zone plate array increases the total object space field of view of the imaging system, and solves the problem of small field of view in the zone plate imaging-based defect detection system, which cannot meet the mass production requirements of the industry. It can be seen that the defect detection system based on zone plate array imaging provided by this application has the advantages of low cost, simple manufacturing of optical elements, simple optical path alignment, high imaging resolution, high yield, and wide wavelength application range.

[0048] In order to form the same structure, those skilled in the art can also design methods that are not exactly the same as the methods described above. In addition, although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0049] The above describes the embodiments of this disclosure. However, these embodiments are only for illustrative purposes and not for limiting the scope of this disclosure. The scope of this disclosure is defined by the appended claims and their equivalents. Without departing from the scope of this disclosure, those skilled in the art can make various substitutions and modifications, and these substitutions and modifications should all fall within the scope of this disclosure.

Claims

1. A defect detection system based on zone plate array imaging, characterized in that, Comprising: A light source, a zone plate array, and an image acquisition component; wherein, the zone plate array is formed by arranging a plurality of zone plate units, and the imaging regions of different zone plate units are separated from each other; Multiple beams of light emitted by the light source pass through the object to be measured and then enter each zone plate unit on the zone plate array respectively to form a converging light field, and the converging light field corresponding to each zone plate unit propagates to the image acquisition component and is received and imaged.

2. The defect detection system based on zone plate array imaging according to claim 1, characterized in that, The system further includes a cavity, the light source is hermetically connected to the cavity, and the zone plate array and the image acquisition component are arranged in the cavity.

3. The defect detection system based on zone plate array imaging according to claim 2, characterized in that, The cavity is a vacuum cavity.

4. The defect detection system based on zone plate array imaging according to claim 3, characterized in that, The system further includes a vibration isolation table, and the vacuum cavity is arranged on the vibration isolation table.

5. The defect detection system based on zone plate array imaging according to claim 4, characterized in that, The vibration isolation table provides 90% vibration isolation at 2 Hz.

6. The defect detection system based on zone plate array imaging according to claim 2, characterized in that, High-purity nitrogen is introduced into the cavity for gas bath protection.

7. The defect detection system based on zone plate array imaging according to claim 1, characterized in that, The target surface area of the image acquisition component is greater than or equal to the imaging area of the zone plate array.

8. The defect detection system based on zone plate array imaging according to claim 7, characterized in that, The image acquisition component includes at least one CCD camera.

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