An umbrella cover type infrared radiation absorption enhancement structure with an upper layer and a preparation method thereof

Abstract

The application relates to an upper umbrella cover type infrared radiation absorption enhancement structure and a preparation method thereof. The upper umbrella cover type infrared radiation absorption enhancement structure comprises a heat-sensitive layer, an upper umbrella cover structure connected with the heat-sensitive layer through an umbrella column and suspended above the heat-sensitive layer to form a closed light-heat coupling space, the upper umbrella cover structure is a conformal three-layer composite structure to form a complete umbrella-shaped absorber, the three-layer composite structure comprises a bottom silicon nitride medium layer, an intermediate titanium layer and a top silicon nitride medium layer arranged in sequence from bottom to top, the umbrella column is a silicon nitride-titanium-silicon nitride composite structure comprising a titanium metal column and a silicon nitride layer, the center of the umbrella column is embedded with the titanium metal column, the periphery of the umbrella column is wrapped with the silicon nitride layer, and the titanium metal column is electrically connected with the intermediate titanium layer. The average absorption rate of the application in the long-wave infrared band is significantly improved, the absorption rate is higher than that of a traditional single medium umbrella cover structure, and the problem of insufficient absorption area under a small pixel size is effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of uncooled infrared detection technology, and specifically relates to an infrared radiation absorption enhancement structure with an upper umbrella-shaped cover and its preparation method. Background Technology

[0002] Uncooled infrared focal plane array sensors are widely used in security monitoring, vehicle infrared imaging, industrial temperature measurement, and consumer electronics due to their advantages such as no need for cooling devices, small size, low power consumption, and controllable cost. Their core detection principle is to achieve photo-thermal conversion through the absorption of infrared radiation, and to output an electrical signal by utilizing the resistance change of the thermistor material (such as vanadium oxide (VOX) or amorphous silicon). Therefore, the infrared absorption efficiency directly determines the sensor's key performance indicators such as detection sensitivity and noise equivalent temperature difference (NETD).

[0003] As sensor pixel sizes gradually shrink (currently the mainstream is 10~25μm), the effective absorption area decreases sharply. How to improve infrared absorption efficiency within a limited space has become a technical bottleneck in the industry. Existing infrared absorption enhancement schemes are mainly divided into two categories: film layer composite and micro / nano structure modulation. Film layer composite schemes mostly use carbon-based nanomaterials (carbon nanotubes, graphene) combined with polymers. Although the cost is low, the thermal stability is poor, and long-term operation is prone to agglomeration and shedding. Micro / nano structure schemes (such as black silicon nanotextured surfaces and metamaterial absorbers) have higher absorption efficiency, but the fabrication process is complex, the compatibility with existing CMOS processes is insufficient, and the structural mechanical strength is difficult to adapt to the sensor packaging and usage scenarios.

[0004] Some existing technologies attempt to expand the absorption area using an upper canopy structure, but these canopies are mostly single dielectric or metal layer structures: single dielectric layers (such as silicon nitride) have limited intrinsic infrared absorption capabilities, especially in the long-wave infrared band where the absorption rate is usually below 60%; single metal layers (such as gold or aluminum) have excessively high reflectivity, and although absorption can be improved through ultra-thinning, it is difficult to balance conductivity and structural stability. In addition, traditional canopy structures suffer from uneven heat conduction, meaning that the absorbed infrared heat cannot be efficiently and evenly transferred to the underlying thermistor layer, resulting in poor sensor response consistency and affecting imaging quality.

[0005] Therefore, there is an urgent need to design an upper canopy structure that is compatible with uncooled infrared focal plane sensors, which can achieve efficient infrared absorption through the synergy of structure and materials, and also meet the requirements of low thermal conductivity, process compatibility, structural stability and uniform heat conduction, thus resolving the contradiction between performance and practicality of existing technologies. Summary of the Invention

[0006] To address the problems of low absorption efficiency, poor thermal stability, uneven heat conduction, and insufficient process compatibility in existing uncooled infrared focal plane array sensors, the present invention aims to provide an infrared radiation absorption enhancement structure with an upper umbrella-type cover, its preparation method, and the preparation method thereof. The invention provides a silicon nitride-titanium-silicon nitride three-layer composite upper umbrella structure. Through the synergistic design of the dielectric layer and the metal layer, combined with the spatial structural advantages of the umbrella, it achieves efficient absorption of infrared radiation, uniform heat conduction, and structural stability. Simultaneously, it is compatible with existing wafer-level fabrication processes, reducing mass production costs.

[0007] To solve the above-mentioned technical problems, the present invention provides an infrared radiation absorption enhancement structure with an upper umbrella-shaped cover, comprising: Thermosensitive layer; The upper umbrella structure is connected to the heat-sensitive layer through the umbrella base and suspended above the heat-sensitive layer to form a closed photothermal coupling space; the upper umbrella structure is a conformally fitted three-layer composite structure to form a complete umbrella-shaped absorber; the three-layer composite structure includes a bottom silicon nitride dielectric layer, a middle titanium metal layer and a top silicon nitride dielectric layer arranged from bottom to top. The umbrella-shaped support is a silicon nitride-titanium-silicon nitride composite structure, comprising a titanium metal pillar and a silicon nitride layer; the titanium metal pillar is embedded in the center and surrounded by the silicon nitride layer, and the titanium metal pillar is electrically connected to the intermediate titanium metal layer.

[0008] Preferably, the thickness of the bottom silicon nitride dielectric layer is 10nm~100nm, the thickness of the top silicon nitride dielectric layer is 10nm~100nm, and the thickness of the intermediate titanium layer is 10nm~50nm.

[0009] Preferably, the diameter of the titanium metal pillar is 2.5μm to 3.5μm, and the thickness of the silicon nitride layer is 20nm to 200nm.

[0010] Preferably, the horizontal projected area of ​​the upper umbrella structure is 1.2 to 2.5 times the area of ​​the thermosensitive layer, and the vertical distance between the upper umbrella structure and the thermosensitive layer is 0.5 μm to 1 μm.

[0011] Preferably, the bottom silicon nitride dielectric layer, the top silicon nitride dielectric layer, and the silicon nitride layer are all prepared using LPCVD technology, with a refractive index of 1.8~2.1, a density ≥95%, and a thermal conductivity ≤0.8 W·m. -1 ·K -1 The high Young's modulus is ≥200GPa; both the intermediate titanium metal layer and the titanium metal pillar are prepared by magnetron sputtering PVD process, with a purity ≥99.9% and a surface roughness ≤5nm.

[0012] This invention also provides a method for fabricating an upper umbrella-type infrared radiation absorption enhancement structure to prepare an upper umbrella-type infrared radiation absorption enhancement structure as described above, comprising: fabrication of a thermistor layer, fabrication of an umbrella and umbrella support structure, and release of a sacrificial layer; the fabrication of the umbrella and umbrella support structure comprises: firstly depositing silicon nitride using LPCVD process, depositing a titanium metal layer using magnetron sputtering PVD process, then depositing silicon nitride a second time using LPCVD process, and etching it using photolithography and ICP-RIE process to adapt to wafer-level CMOS process.

[0013] Preferably, the fabrication of the thermosensitive layer includes: A vanadium oxide thermistor layer with a thickness of 10 nm to 100 nm was sputtered onto the main surface of the bridge deck. After annealing at 250 °C to 350 °C and holding at that temperature for 40 min to 80 min, its sheet resistance was adjusted. Subsequently, the thermistor layer pattern was defined by photolithography and etching processes, and an electrode lead-out structure was prepared.

[0014] Preferably, the fabrication of the umbrella canopy and umbrella base structure includes: First, a polyimide sacrificial layer is deposited and planarized to complete the via etching; A silicon nitride dielectric layer with a thickness of 10nm~100nm was deposited on the surface of the sacrificial layer using LPCVD process, covering the surface of the thermistor layer and the sacrificial layer. A titanium intermediate layer with a thickness of 10 nm to 50 nm was deposited on the surface of the underlying silicon nitride dielectric layer using magnetron sputtering PVD process. The sputtering power was controlled at 80 W to 120 W and the argon atmosphere pressure was 0.5 Pa to 1.0 Pa to ensure the uniformity of the titanium layer. The top silicon nitride dielectric layer with a thickness of 10nm~100nm was deposited again using the LPCVD process, forming a complete composite film system with the bottom silicon nitride dielectric layer and the intermediate titanium metal layer. The composite film system is etched using photolithography and ICP-RIE processes to form an umbrella-shaped structure with an umbrella base. The umbrella base is connected to the thermal layer and located above the thermal layer.

[0015] Preferably, the sacrificial layer release includes: The sacrificial layer is removed by oxygen plasma ashing process with a radio frequency power of 100W~300W, a chamber pressure of 10Pa~50Pa, an oxygen volume flow rate of 50sccm~200sccm, and an ashing time of 5min~20min, so that the upper umbrella structure is suspended above the thermosensitive layer to form a preset gap.

[0016] The present invention also provides an application of an uncooled infrared focal plane sensor, including an infrared radiation absorption enhancement structure with an upper umbrella as described above, which is particularly suitable for long-wave infrared (8~14μm) band detection scenarios, and can significantly improve the sensor’s absorption efficiency of infrared radiation, while taking into account low thermal conductivity and structural stability.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved infrared absorption efficiency: The three-layer composite umbrella structure achieves a significant improvement in average absorption rate in the long-wave infrared (8~14μm) band through the synergistic effect of absorption by the silicon nitride dielectric layer and free carrier absorption by the titanium metal layer, combined with the plasma resonance effect of the silicon nitride-titanium-silicon nitride structure. This is higher than the absorption rate of the traditional single dielectric umbrella structure, effectively solving the problem of insufficient absorption area under small pixel size.

[0018] 2. Uniform and efficient heat conduction: The integrated design of the titanium metal pillars and the intermediate titanium layer of the umbrella pier forms a directional heat conduction channel, which evenly and quickly transfers the heat absorbed by the umbrella canopy to the heat-sensitive layer, avoiding the heat accumulation and uneven conduction problems of traditional umbrella canopy structures, and improving the consistency of sensor response.

[0019] 3. Excellent compatibility between structure and thermal performance: The upper and lower silicon nitride layers have high mechanical strength and low thermal conductivity, which can serve as the support for the umbrella structure and form an integrated thermal isolation system with the microbridge support structure to reduce heat diffusion to the substrate; the thickness of the middle titanium layer is precisely controlled, taking into account both absorption performance and structural stability, avoiding oxidation or shedding of the metal layer, and extending the service life of the device.

[0020] 4. Strong process compatibility and controllable mass production cost: All preparation steps adopt existing wafer-level processes (LPCVD, PVD magnetron sputtering, photolithography, ICP-RIE), without the need to introduce special equipment. It is fully compatible with the traditional preparation process of uncooled infrared focal plane sensors, enabling wafer mass production and significantly reducing preparation costs. Attached Figure Description

[0021] Figure 1 This is a cross-sectional schematic diagram of the upper umbrella-type infrared absorption structure in an embodiment of the present invention; Figure 2 This is a top view of the upper umbrella structure in an embodiment of the present invention.

[0022] In the diagram: 1-thermal layer, 2-upper umbrella structure, 21-bottom silicon nitride dielectric layer, 22-middle titanium metal layer, 23-top silicon nitride dielectric layer, 3-umbrella pier, 31-titanium metal pillar, 32-silicon nitride layer. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0024] like Figure 1 and Figure 2 As shown, this embodiment of the invention specifically provides an upper umbrella-type infrared radiation absorption enhancement structure for an uncooled infrared focal plane array sensor, including a thermistor layer 1; an upper umbrella structure 2 is connected to the thermistor layer 1 via an umbrella support 3, and the upper umbrella structure 2 is suspended above the thermistor layer 1 to form a closed photothermal coupling space; the upper umbrella structure 2 is a three-layer composite structure, consisting of a bottom silicon nitride dielectric layer 21, a middle titanium metal layer 22, and a top silicon nitride dielectric layer 23 from bottom to top, with the three layers conformally bonded to form a complete umbrella-shaped absorber.

[0025] Furthermore, the thickness of the bottom silicon nitride dielectric layer 21 is 10~100nm, the thickness of the top silicon nitride dielectric layer 23 is 10~100nm, and the thickness of the middle titanium layer 22 is 10~50nm; the total thickness of the three-layer composite structure is 100~250nm, the horizontal projected area of ​​the upper umbrella structure 2 is 1.2~2.5 times the area of ​​the lower thermistor layer 1, and the vertical distance between the upper umbrella structure 2 and the thermistor layer 1 is 0.5~1μm.

[0026] Furthermore, the bottom silicon nitride dielectric layer 21 and the top silicon nitride dielectric layer 23 are prepared using a low-pressure chemical vapor deposition (LPCVD) process, with a refractive index of 1.8~2.1, a density ≥95%, and low thermal conductivity (≤0.8 W·m). -1 ·K -1 With a high Young's modulus (≥200GPa), it can serve as a structural support layer and enhance the capture of mid- and long-wave infrared radiation.

[0027] Furthermore, the intermediate titanium layer 22 is prepared by magnetron sputtering PVD process, with a purity ≥99.9% and a surface roughness ≤5nm. As a metal absorption layer, the titanium layer enhances infrared radiation absorption through free carrier absorption. At the same time, it forms a dielectric-metal-dielectric-metal composite structure with the upper and lower silicon nitride layers, which can improve infrared absorption efficiency.

[0028] Furthermore, the umbrella support 3 is a silicon nitride-titanium-silicon nitride composite structure, with a titanium metal pillar 31 embedded in its center and a silicon nitride layer 32 wrapped around it. The titanium metal pillar 31 is electrically connected to the intermediate titanium metal layer 22 and also serves as a heat conduction channel to efficiently transfer the infrared heat absorbed by the umbrella cover to the heat-sensitive layer, avoiding heat loss caused by heat accumulation. The diameter of the umbrella support 3 is 2~5μm, and its height is consistent with the vertical distance between the umbrella cover and the heat-sensitive layer.

[0029] This invention also provides a method for preparing an upper umbrella-shaped infrared radiation absorption enhancement structure, comprising the following steps: Step S1, Preparation of the thermal layer: Sputtering vanadium oxide (VO2) x The thermistor layer, with a thickness controlled at 10~100nm, is annealed (250~350℃, held for 40~80min) to adjust its sheet resistance. Then, the pattern of the thermistor layer is defined by photolithography and etching processes, and the electrode lead-out structure is prepared.

[0030] Step S2, preparation of the umbrella structure: First, a sacrificial layer (polyimide) is deposited and planarized to complete the via etching. Then, an LPCVD process is used to deposit a bottom silicon nitride dielectric layer with a thickness of 10-100 nm on the surface of the sacrificial layer, covering the thermistor layer and the sacrificial layer surface. Next, a titanium layer with a thickness of 10-50 nm is deposited on the surface of the bottom silicon nitride layer using magnetron sputtering, with sputtering power controlled at 80-120 W and argon atmosphere pressure at 0.5-1.0 Pa to ensure the uniformity of the titanium layer. Finally, an LPCVD process is used again to deposit a top silicon nitride dielectric layer with a thickness of 10-100 nm, forming a complete composite film system with the bottom silicon nitride layer and the titanium layer. The composite film system is then etched using photolithography and ICP-RIE (inductively coupled plasma reactive ion etching) to form a canopy and support structure. The support structure is connected to the thermistor layer and located above it.

[0031] Step S3, Sacrificial Layer Release: The sacrificial layer is removed using an oxygen plasma ashing process with a radio frequency power of 100~300W, a chamber pressure of 10~50Pa, an oxygen volume flow rate of 50~200sccm, and an ashing time of 5~20min, so that the umbrella structure is suspended above the thermosensitive layer, forming a preset gap.

[0032] To further illustrate a preferred embodiment of the present invention, this embodiment provides an upper umbrella-type infrared absorption structure for an uncooled infrared focal plane sensor, adapted to a pixel size of 1025μm×768μm, with the following specific parameters: The three-layer composite parameters of the upper canopy structure 2 are as follows: the bottom silicon nitride dielectric layer 21 has a thickness of 10~100nm, the top silicon nitride dielectric layer 23 has a thickness of 10~100nm, the middle titanium layer 22 has a thickness of 30~50nm, and the total thickness is 50~250nm; the horizontal projected area of ​​the canopy is 800μm. 2 (32μm×25μm), which is the area of ​​the thermal layer (625μm). 2 1.28 times that of the heat-sensitive layer, and the vertical distance between the umbrella cover and the heat-sensitive layer is 1μm.

[0033] The umbrella pier 3 has a diameter of approximately 2-5 μm, the titanium metal column 31 has a diameter of 2.5-3.5 μm, and the silicon nitride layer 32 has a thickness of 20-200 nm. The titanium metal column is seamlessly connected to the intermediate titanium metal layer 22, and the heat conduction efficiency is improved by 50% compared with the traditional silicon nitride umbrella pier.

[0034] The preparation process in this embodiment strictly follows the above steps. The sputtering parameters for the titanium layer are: sputtering power 100W, argon pressure 0.8Pa, deposition rate 0.5nm / s, ensuring a surface roughness of 3.2nm for the titanium layer. The sacrificial layer is made of polyimide with a thickness of 0.5~1μm. The oxygen plasma ashing power is 100~300W, and the ashing time is 5~20min, ensuring that the sacrificial layer is completely removed without any residue.

[0035] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A structure for enhancing infrared radiation absorption with an upper umbrella-shaped canopy, characterized in that, include: Thermosensitive layer (1); The upper umbrella structure (2) is connected to the thermosensitive layer (1) through the umbrella block (3) and suspended above the thermosensitive layer (1) to form a closed photothermal coupling space; the upper umbrella structure (2) is a conformally fitted three-layer composite structure to form a complete umbrella-shaped absorber; the three-layer composite structure includes a bottom silicon nitride dielectric layer (21), a middle titanium metal layer (22) and a top silicon nitride dielectric layer (23) arranged from bottom to top. The umbrella pier (3) is a silicon nitride-titanium-silicon nitride composite structure, including a titanium metal pillar (31) and a silicon nitride layer (32); the titanium metal pillar (31) is embedded in the center and the silicon nitride layer (32) is wrapped around the periphery. The titanium metal pillar (31) is electrically connected to the intermediate titanium metal layer (22).

2. The infrared radiation absorption enhancement structure with an upper umbrella-shaped cover as described in claim 1, characterized in that, The thickness of the bottom silicon nitride dielectric layer (21) is 10nm~100nm, the thickness of the top silicon nitride dielectric layer (23) is 10nm~100nm, and the thickness of the intermediate titanium metal layer (22) is 10nm~50nm.

3. The infrared radiation absorption enhancement structure with an upper umbrella-shaped cover as described in claim 1, characterized in that, The titanium metal pillar (31) has a diameter of 2.5μm to 3.5μm, and the silicon nitride layer (32) has a thickness of 20nm to 200nm.

4. The infrared radiation absorption enhancement structure with an upper umbrella-shaped cover as described in claim 1, characterized in that, The horizontal projected area of ​​the upper umbrella structure (2) is 1.2 to 2.5 times the area of ​​the thermal layer (1), and the vertical distance between the upper umbrella structure (2) and the thermal layer (1) is 0.5 μm to 1 μm.

5. The infrared radiation absorption enhancement structure with an upper umbrella-shaped cover as described in claim 1, characterized in that, The bottom silicon nitride dielectric layer (21), the top silicon nitride dielectric layer (23), and the silicon nitride layer (32) are all prepared by LPCVD process, with a refractive index of 1.8~2.1, a density ≥95%, and a thermal conductivity ≤0.8W·m. -1 ·K -1 The high Young's modulus is ≥200GPa; the intermediate titanium layer (22) and the titanium metal pillar (31) are both prepared by magnetron sputtering PVD process, with a purity ≥99.9% and a surface roughness ≤5nm.

6. A method for preparing an infrared radiation absorption enhancement structure with an upper umbrella-shaped cover, as described in any one of claims 1 to 5, characterized in that, include: Preparation of the heat-sensitive layer, preparation of the canopy and pier structure, and release of the sacrificial layer; The fabrication of the canopy and support structure includes: firstly, depositing silicon nitride using LPCVD process, depositing a titanium metal layer using magnetron sputtering PVD process, then depositing silicon nitride again using LPCVD process, and finally etching it using photolithography and ICP-RIE process to adapt to wafer-level CMOS process.

7. The method for preparing a structure with an upper umbrella-shaped infrared radiation absorption enhancement as described in claim 6, characterized in that, The fabrication of the thermosensitive layer includes: A vanadium oxide thermistor layer is sputtered with a thickness controlled at 10 nm to 100 nm. After annealing at 250 °C to 350 °C and holding at that temperature for 40 min to 80 min, its sheet resistance is adjusted. Subsequently, the thermistor layer pattern is formed by photolithography and etching processes, and an electrode lead-out structure is prepared.

8. The method for preparing a structure with an upper umbrella-shaped infrared radiation absorption enhancement as described in claim 6, characterized in that, The fabrication of the umbrella canopy and umbrella base structure includes: First, a polyimide sacrificial layer is deposited and planarized to complete the via etching; A silicon nitride dielectric layer with a thickness of 10nm~100nm was deposited on the surface of the sacrificial layer using LPCVD process, covering the surface of the thermistor layer and the sacrificial layer. A titanium intermediate layer with a thickness of 10 nm to 50 nm was deposited on the surface of the underlying silicon nitride dielectric layer using magnetron sputtering PVD process. The sputtering power was controlled at 80 W to 120 W and the argon atmosphere pressure was 0.5 Pa to 1.0 Pa to ensure the uniformity of the titanium layer. The top silicon nitride dielectric layer with a thickness of 10nm~100nm was deposited again using the LPCVD process, forming a complete composite film system with the bottom silicon nitride dielectric layer and the intermediate titanium metal layer. The composite film system is etched using photolithography and ICP-RIE processes to form an umbrella-shaped structure with an umbrella base. The umbrella base is connected to the thermal layer and located above the thermal layer.

9. The method for preparing a superstructure with an upper umbrella-shaped infrared radiation absorption enhancement structure as described in claim 6, characterized in that, The sacrificial layer release includes: The sacrificial layer is removed by oxygen plasma ashing process with a radio frequency power of 100W~300W, a chamber pressure of 10Pa~50Pa, an oxygen volume flow rate of 50sccm~200sccm, and an ashing time of 5min~20min, so that the upper umbrella structure is suspended above the thermosensitive layer to form a preset gap.

10. An application of an uncooled infrared focal plane sensor, characterized in that, Including a superstructure-type infrared radiation absorption enhancement structure as described in any one of claims 1 to 5, suitable for detection scenarios in the 8μm~14μm long-wave infrared band.

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