Infrared image enhancement method and system

Abstract

The invention relates to the technical field of semiconductors, and discloses an infrared image enhancement method and system.The method comprises the steps that a layer of refractive index matching medium is temporarily applied to the surface of an observation area of a covering layer of a sample to be detected, and a refractive index matching medium layer is formed; the sample to be tested at least comprises a semiconductor substrate and a covering layer covering the semiconductor substrate; when the infrared light source irradiates the refractive index matching medium, the infrared imaging objective lens is optically matched with the refractive index matching medium layer to form a variable light path; and performing image acquisition on the observation area by using the infrared camera through the variable light path to obtain a detection image of the to-be-detected sample. Through refractive index matching, Fresnel reflection loss of a covering layer and an air interface and scattering caused by surface roughness are greatly reduced, incident light can enter and leave a sample more efficiently, negative effects of the covering layer are overcome, and infrared imaging definition is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an infrared image enhancement method and system. Background Technology

[0002] In the semiconductor industry, infrared transmission imaging technology is a key means for non-destructive testing and failure analysis of the internal structure of wafers and chips. It utilizes the characteristic that infrared light of a specific wavelength can penetrate semiconductor materials such as silicon substrates to observe key areas such as below the metal wiring layer, inside silicon vias, solder joint interfaces, and internal defects. However, in practical applications, the surface of the sample to be tested is often covered with various functional or protective films, such as ultraviolet curable adhesive films used in wafer dicing, epoxy molding compounds used in chip packaging, temporary bonding adhesive layers, or protective layers deposited in the process, or the presence of a cover layer on the chip surface itself, which seriously degrades the infrared imaging quality. The main reasons are: (1) Light scattering caused by surface roughness: The surface of the cover layer is not an ideal optical plane at the microscopic level. Its roughness will cause the incident and outgoing infrared light to be scattered, resulting in signal attenuation and image blurring. (2) Fresnel reflection caused by refractive index mismatch: There is a large refractive index difference between the cover layer and air, which leads to significant Fresnel reflection at the interface, reduces the effective incident light intensity, and may produce interfering reflected light spots or ghosting. (3) Non-uniformity of the coating layer itself: Microscopic non-uniformity of film thickness or material will generate additional optical interference and reduce the signal-to-noise ratio of the image.

[0003] Existing technologies typically compensate for these problems partially by improving the sensitivity of infrared cameras, increasing the power of light sources, or performing complex image post-processing. However, these methods are costly, have limited effectiveness, and cannot fundamentally eliminate the inherent optical interference caused by the interface of the overlay layer. Therefore, how to effectively overcome the negative effects of the overlay layer and significantly improve the signal-to-noise ratio and sharpness of infrared imaging is an urgent technical problem to be solved.

[0004] The above content is only used to help understand the technical solution of the present invention and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this invention is to provide an infrared image enhancement method and system, which aims to solve the technical problem in the prior art where the negative impact of the overlay layer leads to poor infrared imaging signal-to-noise ratio and clarity.

[0006] To achieve the above objectives, the present invention provides an infrared image enhancement method, which is applied to an infrared image enhancement system, wherein the infrared image enhancement system includes at least an infrared light source, an infrared imaging objective lens, and an infrared camera. The infrared image enhancement method includes the following steps: A refractive index matching medium is temporarily applied to the surface of the observation area of ​​the cover layer of the sample to be tested to form a refractive index matching medium layer. The sample to be tested includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. When the infrared light source illuminates the refractive index matching medium, the infrared imaging objective lens and the refractive index matching medium layer optically combine to form a variable light path; The infrared camera acquires images of the observation area through the variable light path to obtain a detection image of the sample to be tested.

[0007] Preferably, after acquiring an image of the sample to be tested by using the infrared camera to capture an image of the observation area through the variable light path, the method further includes: The optical coupling is separated, and the refractive index matching medium is removed from the surface of the cover layer.

[0008] Preferably, the infrared light source is a narrowband light source or a tunable light source, and the emission wavelength of the infrared light source is in the range of 750nm~3000um.

[0009] Preferably, the infrared imaging objective is an infrared achromatic objective or a dry objective with a numerical aperture NA ≥ 0.2.

[0010] Preferably, the removal method includes inclined drainage, low-pressure liquid aspiration, gas purging and evaporation of volatile media, or mechanical removal, and purging is performed using dry and clean gas.

[0011] Preferably, during the imaging process, at least one of the following methods is used: partial coherent illumination, introducing optical path jitter, or performing multi-wavelength image acquisition and fusion, in order to suppress interference fringes generated at the interface of the multilayer medium.

[0012] Preferably, the refractive index matching medium includes a high-purity aqueous glycerol solution, a fluorinated liquid, or a high-refractive-index silicon-based gel.

[0013] Preferably, the refractive index matching medium is applied by precise quantitative dispensing, controlled spraying, or spin coating, and the thickness and uniformity of the medium layer are controlled by adjusting the coating parameters.

[0014] Furthermore, to achieve the above objectives, the present invention proposes an infrared image enhancement system, which includes at least: an infrared light source, an infrared imaging objective lens, and an infrared camera; The infrared light source is used to illuminate a refractive index matching medium temporarily applied to the cover layer of the sample under test. The sample under test includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. The refractive index matching medium is applied to the surface of the observation area of ​​the cover layer of the sample under test. The infrared imaging objective lens is used to optically combine with the refractive index matching medium layer to form a variable light path; The infrared camera is used to acquire images of the observation area through the variable light path to obtain a detection image of the sample to be tested.

[0015] Preferably, the system further includes a container and piping for holding or circulating the refractive index matching medium.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] 1) Significantly improved performance: By matching the refractive index, the Fresnel reflection loss at the interface between the coating layer and the air and the scattering caused by surface roughness are greatly reduced, allowing incident light to enter and leave the sample more efficiently, resulting in an order-of-magnitude improvement in image brightness, contrast and signal-to-noise ratio.

[0018] 2) Strong versatility of principle: This method does not depend on specific film materials. As long as there is imaging degradation caused by refractive index mismatch and surface roughness, this method can be applied to improve it.

[0019] 3) Safe and non-destructive: The use of chemically mild media (such as water) and non-contact removal methods ensures that semiconductor samples are protected from contamination, corrosion or physical damage during the detection process, maintaining the non-destructive nature of the detection.

[0020] 4) Flexible and convenient operation: It can flexibly select and adjust matching media with different refractive indices according to different coating materials and testing requirements, and can be integrated into automated testing equipment to achieve online enhanced testing.

[0021] 5) Enhanced optical performance limits: By combining the matching medium with a high-NA immersion objective lens, the theoretical resolution and light intensity within the depth of field of the system are effectively improved, making it possible to detect even smaller defects.

[0022] 6) Flexible and compatible imaging modes: This method can be combined with a variety of advanced infrared microscopy modes (such as photoluminescence and infrared spectral imaging) to provide a universal front-end signal enhancement interface. Attached Figure Description

[0023] Figure 1 This is a first structural schematic diagram of the infrared image enhancement system of the hardware operating environment involved in the embodiments of the present invention; Figure 2 This is a flowchart illustrating the first embodiment of the infrared image enhancement method of the present invention; Figure 3 This is a schematic diagram of the second structure of the infrared image enhancement system in the hardware operating environment involved in the embodiments of the present invention; Figure 4This is the pre-enhanced detection image of the sample to be tested; Figure 5 This is an enhanced detection image of the sample to be tested in an embodiment of the infrared image enhancement method of the present invention.

[0024] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] Reference Figure 1 , Figure 1 This is a first structural schematic diagram of the infrared image enhancement system of the hardware operating environment involved in the embodiments of the present invention. Figure 1 As shown, the infrared image enhancement system includes at least an infrared light source, an infrared imaging lens, and an infrared camera.

[0027] Based on the above hardware structure, an embodiment of the infrared image enhancement method of the present invention is proposed.

[0028] Reference Figure 2 The first embodiment of the infrared image enhancement method of the present invention is proposed.

[0029] In a first embodiment, the infrared image enhancement method includes the following steps: Step S10: Temporarily apply a refractive index matching medium to the surface of the observation area of ​​the cover layer of the sample to be tested to form a refractive index matching medium layer. The sample to be tested includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate.

[0030] Step S20: When the infrared light source illuminates the refractive index matching medium, the infrared imaging objective lens and the refractive index matching medium layer optically combine to form a variable light path.

[0031] Step S30: Using the infrared camera, the observation area is captured through the variable light path to obtain the detection image of the sample to be tested.

[0032] It should be understood that, as Figure 1 As shown, on the surface of the observation area of ​​the overlay layer, a refractive index matching medium can be applied below the infrared imaging objective lens to form a refractive index matching medium layer. For example... Figure 3 As shown, Figure 3This is a second structural schematic diagram of the infrared image enhancement system in the hardware operating environment involved in the embodiments of the present invention. Alternatively, a refractive index matching medium layer can be temporarily applied directly above the sample cover layer to form a refractive index matching medium layer. The front optical surface of the infrared imaging objective or a dedicated optical coupling window is optically contacted or aligned (not in contact) with the refractive index matching medium layer, forming a variable optical path from the objective to the sample cover layer. The sample is illuminated using the infrared light source, and the infrared camera acquires an image of the observation area through the coupled optical path. During imaging, interface scattering and reflection are suppressed by the refractive index matching medium layer. The detection image before infrared image enhancement using the method of this embodiment is shown below. Figure 4 As shown, the image is not clear. After using the method of this embodiment, as... Figure 5 As shown, this is an enhanced detection image of the sample to be tested acquired in this embodiment, and the image is clearer.

[0033] It should be understood that a layer that is too thin cannot effectively fill roughness, while a layer that is too thick introduces unnecessary absorption and increases aberrations. The thickness is preferably controlled using a precision quantitative coating device. Preferably, the refractive index n_m of the refractive index matching medium and the refractive index n_c of the coating layer satisfy: |n_m-n_c| / n_c≤0.1, which provides better results. Other values ​​are also acceptable, and this embodiment does not impose any limitations on this. Preferably, the thickness d_m of the refractive index matching medium layer satisfies: 10μm≤d_m≤2mm, which provides better results. Other values ​​are also acceptable, and this embodiment does not impose any limitations on this.

[0034] The refractive index matching medium includes high-purity glycerol aqueous solution, fluorinated liquid or high refractive index silicon-based gel, etc., and may also be other media. This embodiment does not limit this.

[0035] Furthermore, in one embodiment, the infrared imaging objective is an infrared achromatic objective or a dry objective with a numerical aperture NA ≥ 0.2; the infrared light source is a narrowband light source or a tunable light source, and the emission wavelength of the infrared light source is in the range of 750 nm to 3000 μm.

[0036] Understandably, the light source optimization involves using a narrowband light source or a tunable laser whose emission wavelength is located within the infrared transparent window of the semiconductor substrate and avoids the main absorption peaks of the capping layer and the matching medium.

[0037] Objective lens optimization: Infrared achromatic objectives with a numerical aperture (NA) ≥ 0.2 are preferred, and their aberration correction band covers the selected imaging wavelength. Combining high NA objectives with a refractive index-matching medium significantly improves the system's light-gathering capability and resolution.

[0038] Illumination optimization: Employ one or more of the following methods: coaxial incident illumination, dark field illumination, or differential interference contrast illumination, combined with refractive index matching technology, to enhance contrast sensitivity to specific types of defects.

[0039] In a specific implementation, the sample to be tested can be a wafer that has been cut but not yet picked up, with the chip fixed by a UV film adhesive layer. The UV film surface faces upward, and the front side (circuit side) of the chip faces downward. Therefore, the method of this embodiment can be used for highly sensitive and contamination-free detection of internal hidden cracks in chips that remain attached to the UV film after wafer cutting.

[0040] The system can be configured to use an inverted infrared microscope, with the infrared light source and infrared camera positioned above the sample to be tested, and a long working distance infrared objective lens.

[0041] Sample fixation: The UV film frame with the wafer attached is inverted and mounted on a dedicated sample holder, ensuring the chip face down and the UV film substrate face up. The sample holder only supports the edges of the frame, leaving the observation area suspended and flat.

[0042] Selection of refractive index matching medium: It can be a high-purity glycerol aqueous solution, which usually refers to a glycerol aqueous solution with a glycerol content of more than 80%.

[0043] Furthermore, in one embodiment, the optical contact includes direct immersion coupling, window coupling achieved through an infrared transparent optical window, or non-contact optical coupling.

[0044] It should be noted that direct immersion coupling involves using a specially designed immersion infrared objective lens, whose front lens is directly immersed in the refractive index matching medium layer. Optical window coupling involves introducing a planar, parallel infrared transparent optical window (such as a zinc selenide, germanium, or silicon window) between the infrared imaging objective and the sample. The refractive index matching medium is first filled between the window and the cover layer, and then the infrared imaging objective images the upper surface of the window or the image behind the window. Incomplete immersion coupling involves coating the surface of the object under test with the refractive index matching medium layer, but not directly contacting the infrared objective lens; air is filled in between or a vacuum environment is used, and then imaging is performed.

[0045] In this embodiment, optical coupling can be achieved by controlling the infrared imaging objective lens to move upwards to reach the focusing position, at which point it achieves immersion or non-immersion coupling with the glycerol aqueous solution medium layer. For example, a narrowband LED light source with a wavelength of 1350nm is used for coaxial incident illumination. This wavelength has good silicon penetration and low medium absorption. Image acquisition: Compared with dry detection without using a medium, the image signal-to-noise ratio is significantly improved. Microcracks that were originally invisible, extending from the back of the chip to a depth of several micrometers, appear as clear bright white linear features with significant contrast.

[0046] The fundamental reason for the blurred image when infrared light passes through a rough protective film is that, under normal conditions, the refractive index of air (n) is 0.1, while the refractive index (n) of the film material is approximately between 1.4 and 1.6. The refractive index difference at the air-rough film interface is about 0.5, and the difference at the film-wafer interface is about 0.1. These differences are the cause of image deterioration. The core mechanism of refractive index matching is to uniformly apply a coupling liquid with the same refractive index as the film onto the test object. This replaces the original air-film interface with a liquid-film interface, greatly reducing the refractive index difference and minimizing interference from scattered light on the image.

[0047] Furthermore, in one embodiment, after step S30, the method further includes: The optical coupling is separated, and the refractive index matching medium is removed from the surface of the cover layer.

[0048] Furthermore, in one embodiment, the removal methods include inclined drainage, low-pressure liquid aspiration, gas purging and evaporation of volatile media, or mechanical removal, and purging is performed using dry and clean gas.

[0049] In specific implementations, the removal of the refractive index-matching medium can employ physical methods tailored to the properties of the medium. For non-volatile media, inclined drainage combined with low-pressure liquid aspiration is preferred, followed by purging of the residual thin layer with dry gas. For volatile media, gas purging and evaporation or mechanical removal can be used, specifically low-temperature heating-assisted evaporation and inert gas purging. Safe medium removal can also involve: the infrared imaging objective lens retracting from the medium layer; using a low-absorption cellulose sponge for contact adsorption to remove most high-viscosity media; quickly wiping the residue with a lint-free cloth dampened with deionized water; and finally purging with dry nitrogen. The UV film surface remains clean and dry, without affecting subsequent pickup. This embodiment does not limit the specific removal method.

[0050] In this embodiment, a refractive index matching medium is temporarily applied to the surface of the observation area of ​​the cover layer of the sample under test, forming a refractive index matching medium layer. The sample under test includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. When the infrared light source illuminates the refractive index matching medium, the infrared imaging objective lens and the refractive index matching medium layer are optically combined to form a variable light path. Through the variable light path, the infrared camera acquires an image of the observation area to obtain a detection image of the sample under test. By using refractive index matching, Fresnel reflection loss at the interface between the cover layer and the air and scattering caused by surface roughness are greatly reduced, allowing incident light to enter and leave the sample under test more efficiently. Image brightness, contrast, and signal-to-noise ratio are improved by orders of magnitude, overcoming the negative impact of the cover layer and improving the infrared imaging signal-to-noise ratio and clarity.

[0051] Continue to refer to Figure 2Based on the first embodiment described above, a second embodiment of the infrared image enhancement method of the present invention is proposed.

[0052] In this embodiment, the removal methods include inclined drainage, low-pressure liquid aspiration, gas purging and evaporation of volatile media, or mechanical removal, and purging is performed using dry and clean gas.

[0053] Furthermore, in this embodiment, during the imaging process, at least one of the following methods is employed: partial coherent illumination, introducing optical path jitter, or performing multi-wavelength image acquisition and fusion, in order to suppress interference fringes generated at the interface of the multilayer medium.

[0054] It should be noted that, in order to overcome the interference fringes that may be generated by the interface of multiple media, one or more of the following strategies can be adopted: Use partially coherent or low-coherence broadband infrared light sources to reduce interference effects.

[0055] Introduce tiny and controllable optical path jitter in the imaging optical path.

[0056] Multiple images at different wavelengths are acquired and fused.

[0057] Furthermore, in this embodiment, the refractive index matching medium is applied by precise quantitative dispensing, controlled spraying, or spin coating, and the thickness and uniformity of the medium layer are adjusted by controlling the coating parameters.

[0058] In this embodiment, the sample to be tested can be a wafer.

[0059] Optical coupling and imaging: The motion platform is controlled to slowly immerse the tip of the immersion objective into the liquid film (or not) until the optimal working distance is reached. Coaxial incident illumination is used to collect reflected signals from the internal interface. Due to the high NA and perfect refractive index matching, the system's effective resolution approaches the diffraction limit, successfully identifying submicron-level stress-induced cracks on the back side.

[0060] Media removal: After the objective lens is lifted and detached, the platform is tilted at a certain angle, such as 30°, and most of the fluorinated liquid flows away naturally due to its low viscosity. Then, dry nitrogen gas with a low temperature (e.g., -40°C) dew point (e.g., 3 psi pressure) is used to purge the back of the wafer and the stage, and the fluorinated liquid completely evaporates without residue.

[0061] Continue to refer to Figure 2 Based on the first or second embodiment described above, a third embodiment of the infrared image enhancement method of the present invention is proposed.

[0062] The method described in this embodiment can be used for internal observation of ceramic packaged devices with a surface roughness Ra of up to 2 μm. Specifically, it is used for window coupling detection of high-roughness packaged surfaces.

[0063] The system can be configured to use a 1550nm tunable laser, with the wavelength fine-tuned as needed to optimize contrast. A standard mid-infrared objective lens with NA=0.5 is used, with a zinc selenide (ZnSe) plate mounted below it as an optical window.

[0064] Medium application and coupling: The capping layer is a rough ceramic encapsulation (e.g., n≈1.75). A high-refractive-index silicon-based gel (e.g., n=1.72, paste-like) is selected as the refractive index matching medium. An appropriate amount of high-refractive-index silicon-based gel is dotted onto the observation area, and then the optical window is lowered to allow the high-refractive-index silicon-based gel to fill all gaps between the window and the rough encapsulation surface, expelling air bubbles. The refractive index n of the high-refractive-index silicon-based gel is typically in the range of 1~2.

[0065] Imaging: Transmission imaging of the device interior is achieved through an optical window. The gel greatly eliminates diffuse reflection from the rough surface, allowing the laser to effectively penetrate and exit the encapsulation, clearly revealing voids and defects at the internal gold wire bonding points.

[0066] Removal: Raise the optical window; most of the gel will detach with the window. Residual gel, due to its cohesive force, can be gently peeled off entirely with a PTFE scraper. Minimal residue can be wiped away with a specialized cleaner.

[0067] Continue to refer to Figure 2 Based on the first, second, or third embodiment described above, a fourth embodiment of the infrared image enhancement method of the present invention is proposed.

[0068] In this embodiment, the detection of the complex internal structure of a multi-layered stacked chip is carried out due to the numerous interfaces that easily generate interference fringes.

[0069] The system configuration, for example, employs a laser array with rapidly switchable wavelengths (wavelengths: 1200nm, 1300nm, 1450nm, 1550nm) and uses an achromatic infrared objective with NA=0.7.

[0070] Medium and Imaging: The overlay is a polyimide coating (e.g., n≈1.68), and a matching oil (e.g., n=1.65) is used. A direct immersion method is employed. Four images are rapidly acquired sequentially at the same location using four wavelengths.

[0071] Image processing: Since the phase of the interference pattern is different at different wavelengths, the four images are averaged at the pixel level or fused using a specific algorithm, which effectively suppresses the interference noise of the fixed pattern and obtains the final image with uniform background and prominent details, revealing the micron-level alignment deviation between layers.

[0072] Continue to refer to Figure 2Based on the first, second, third, or fourth embodiments described above, a fifth embodiment of the infrared image enhancement method of the present invention is proposed.

[0073] In this embodiment, before step S20, the method further includes: A polarizer is added at the incident point of the infrared light source, and an analyzer is added in front of the infrared imaging objective lens, so that the polarizer and the analyzer are orthogonally polarized to block scattering noise.

[0074] It should be noted that under normal circumstances, defects produce regular projection and reflection of partially polarized light under illumination, while rough film surfaces produce irregular scattering. A light-passing polarized light system can filter out this portion, reducing its impact on imaging. Its main structure is as follows: a polarizer is added at the incident light source, and an analyzer is added in front of the objective lens, ensuring that the polarizer and analyzer are orthogonally polarized, which can block more than 90% of the scattering noise.

[0075] Based on the above method embodiments, this invention proposes an infrared image enhancement system, which includes at least: an infrared light source, an infrared imaging objective lens, and an infrared camera; The infrared light source is used to illuminate a refractive index matching medium temporarily applied to the cover layer of the sample under test. The sample under test includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. The refractive index matching medium is applied to the surface of the observation area of ​​the cover layer of the sample under test. The infrared imaging objective lens is used to optically combine with the refractive index matching medium layer to form a variable light path; The infrared camera is used to acquire images of the observation area through the variable light path to obtain a detection image of the sample to be tested.

[0076] Furthermore, the system also includes containers and piping for holding or circulating the refractive index matching medium.

[0077] Other embodiments or specific implementations of the infrared image enhancement system described in this invention can be found in the above-described method embodiments, and will not be repeated here.

[0078] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0079] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. In the unit claims listing several devices, several of these devices may be embodied by the same hardware item. The use of the terms first, second, and third, etc., does not indicate any order and can be interpreted as identifiers.

[0080] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as a read-only memory image (ROM) / random access memory (RAM), magnetic disk, optical disk), and includes several instructions to cause a terminal device (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0081] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. An infrared image enhancement method, characterized in that, The infrared image enhancement method is applied to an infrared image enhancement system, which includes at least an infrared light source, an infrared imaging objective lens, and an infrared camera. The infrared image enhancement method includes the following steps: A refractive index matching medium is temporarily applied to the surface of the observation area of ​​the cover layer of the sample under test to form a refractive index matching medium layer. The sample under test includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. When the infrared light source illuminates the refractive index matching medium, the infrared imaging objective lens and the refractive index matching medium layer optically combine to form a variable light path; The infrared camera acquires images of the observation area through the variable light path to obtain a detection image of the sample to be tested.

2. The infrared image enhancement method as described in claim 1, characterized in that, After acquiring an image of the sample to be tested by using the infrared camera to capture an image of the observation area through the variable light path, the method further includes: The optical coupling is separated, and the refractive index matching medium is removed from the surface of the cover layer.

3. The infrared image enhancement method as described in claim 1, characterized in that, The infrared light source is a narrowband light source or a tunable light source, and the emission wavelength of the infrared light source is in the range of 750nm~3000um.

4. The infrared image enhancement method as described in claim 1, characterized in that, The infrared imaging objective is an infrared achromatic objective or a dry objective with a numerical aperture (NA) ≥ 0.

2.

5. The infrared image enhancement method as described in claim 2, characterized in that, Removal methods include inclined drainage, low-pressure liquid aspiration, gas purging and evaporation of volatile media, or mechanical removal, with purging performed using dry and clean gas.

6. The infrared image enhancement method as described in claim 1, characterized in that, During the imaging process, at least one of the following methods is employed: partial coherent illumination, introducing optical path jitter, or performing multi-wavelength image acquisition and fusion, in order to suppress interference fringes generated at the interface of multiple media.

7. The infrared image enhancement method as described in claim 1, characterized in that, The refractive index matching medium includes a high-purity aqueous glycerol solution, a fluorinated liquid, or a high-refractive-index silicon-based gel.

8. The infrared image enhancement method according to any one of claims 1 to 7, characterized in that, The refractive index matching medium is applied using precise quantitative dispensing, controlled spraying, or spin coating, and the thickness and uniformity of the medium layer are adjusted by controlling the coating parameters.

9. An infrared image enhancement system, characterized in that, The infrared image enhancement system includes at least: an infrared light source, an infrared imaging objective lens, and an infrared camera; The infrared light source is used to illuminate a refractive index matching medium temporarily applied to the cover layer of the sample under test. The sample under test includes at least a semiconductor substrate and a cover layer covering the semiconductor substrate. The refractive index matching medium is applied to the surface of the observation area of ​​the cover layer of the sample under test. The infrared imaging objective lens is used to optically combine with the refractive index matching medium layer to form a variable light path; The infrared camera is used to acquire images of the observation area through the variable light path to obtain a detection image of the sample to be tested.

10. The infrared image enhancement system as described in claim 9, characterized in that, The system also includes containers and piping for holding or circulating the refractive index matching medium.

Images