Preparation method and application of double-layer micro-bolometer

Abstract

The invention belongs to the technical field of MEMS devices, and particularly relates to a preparation method and application of a double-layer micro-bolometer. According to the preparation method of the double-layer micro-bolometer provided by the invention, aiming at the defect that a second sacrificial layer of thermocuring polyimide which is cured at low temperature is easy to corrode and dissolve, the degumming liquid NMP which is difficult to hydrolyze imide bonds is used in a wet degumming process, so that a deposited optical absorption structure has relatively strong infrared absorption capability, and the thermal conductivity of the double-layer micro-bolometer is improved. The performance of the micro-bolometer is improved; meanwhile, in the wet-method photoresist removing process, a combined photoresist removing solution of an EKC photoresist removing solution and an NMP photoresist removing solution is used for soaking, then the NMP photoresist removing solution is used for stripping, and the advantages of the EKC photoresist removing solution and the NMP photoresist removing solution are combined, so that the detection performance of the double-layer micro-bolometer is further improved; therefore, the technical problem that the performance of the prepared micro-bolometer is reduced due to the fact that the thermocuring polyimide sacrificial layer is easy to corrode and dissolve in the existing preparation process of the micro-bolometer is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of MEMS devices, and particularly relates to a preparation method and application of a double-layer microbolometer. BACKGROUND

[0002] MEMS devices are micro intelligent systems manufactured through semiconductor processes, can integrate sensing, execution, signal processing and other functions on a single chip, and are widely applied in many fields such as consumer electronics, automobile industry and security and protection; for example, a MEMS microphone based on a piezoelectric effect, an automobile tire pressure sensor based on a piezoresistance effect and a microbolometer based on a thermal effect, the microbolometer belonging to a non-refrigeration infrared focal plane detector has advantages such as working at room temperature and not needing a refrigeration device, and becomes an emerging thermal imaging detector.

[0003] A pixel structure of a microbolometer package serves as a basic detection unit, converts infrared radiation energy into an electrical signal through a thermal sensitive layer, and transmits the electrical signal to a substrate of an integrated readout circuit through a conductive layer, and the substrate of the integrated readout circuit receives the electrical signal transmitted by the pixel structure; in order to reduce the interference on the thermal sensitive layer, in the preparation process of the microbolometer, in addition to depositing a passivation layer on the thermal sensitive layer, a suspended thermal isolation structure is also made between the pixel structure of the microbolometer and the substrate of the integrated readout circuit, the preparation of the suspended thermal isolation structure needs to first use a thermosetting polyimide sacrificial layer structure as a temporary support, complete the pattern transfer of the pixel structure on the sacrificial layer through a lithography etching combined with a deposition process, remove the sacrificial layer to form the suspended thermal isolation structure by dicing and releasing, and the substrate of the integrated readout circuit is below the suspended thermal isolation structure, and the thermal sensitive layer, the passivation layer and other structures supported by a support layer are above the suspended thermal isolation structure, the integrated readout circuit of the substrate and the thermal sensitive layer are internally electrically connected through the conductive layer, and finally the microbolometer is packaged and prepared.

[0004] The ability of a microbolometer to sense infrared radiation energy is one of the core factors determining its thermal imaging detection performance. To enhance the ability to sense infrared radiation energy and obtain higher optical absorption, technicians have developed a double-layer microbolometer. The double-layer microbolometer is provided with a second layer of optical absorption structure above the thermal sensitive layer, thereby improving the thermal imaging detection performance of the microbolometer. The second layer of optical absorption structure of the double-layer microbolometer also needs to rely on a second sacrificial layer of thermosetting polyimide as a temporary support during the preparation process. The preparation process of the double-layer microbolometer first prepares a sacrificial layer of thermosetting polyimide on the substrate of the integrated readout circuit, then completes the first layer of microbolometer structure through a photolithography etching combined with a deposition process, next coats a layer of thermosetting polyimide film for the second time, which is thermosetted as a second sacrificial layer of thermosetting polyimide, then completes the patterning transfer and deposition of the optical absorption structure through a photolithography etching combined with a deposition process again, and finally completes the PAD electrode fabrication and dicing release to package and manufacture the double-layer microbolometer. In the preparation process of the double-layer microbolometer, the thermal sensitive layer in the pixel structure has been prepared, so as to reduce the interference on the thermal sensitive layer. At this time, the curing temperature of the second sacrificial layer of thermosetting polyimide cannot be too high, which is usually around 250 DEG C, in the low temperature range of the curing temperature of the thermosetting polyimide. Because the high temperature will cause the thermal sensitive material vanadium oxide (VOx) in the thermal sensitive layer to transform into a metal state, and increase the O vacancies in the vanadium oxide (VOx), which easily leads to the failure of the thermal sensitive layer and the damage of the microbolometer. Therefore, the polyimide as the second sacrificial layer in the preparation process of the double-layer microbolometer is usually low-temperature cured. However, the low-temperature cured thermosetting polyimide has poor internal chemical stability. Although it can provide mechanical support, in the wet stripping step of the photolithography etching process, the EKC830 stripping solution used in the wet stripping process can easily corrode and dissolve the imide bond (-CO-N-CO-) of the thermosetting polyimide while removing the photoresist. This destroys the structure and dimensional stability of the second sacrificial layer of thermosetting polyimide, causing the cavity of the subsequently deposited optical absorption structure to deviate from the design value, the absorption capacity of infrared light decreases, and the performance of the microbolometer is reduced.

[0005] Therefore, it is necessary to develop a preparation process of a double-layer microbolometer to solve the problem that the existing double-layer microbolometer is easily corroded and dissolved in the wet stripping process, which leads to poor performance of the prepared microbolometer. SUMMARY

[0006] Therefore, it is necessary to develop a preparation process of a double-layer microbolometer to solve the problem that the existing double-layer microbolometer is easily corroded and dissolved in the wet stripping process, which leads to poor performance of the prepared microbolometer. SUMMARY

[0006] Therefore, it is necessary to develop a preparation process of a double-layer microbolometer to solve the problem that the existing double-layer microbolometer is easily corroded and dissolved in the wet stripping process, which leads to poor performance of the prepared microbolometer.

[0007] The first aspect of the present application provides a preparation method of a double-layer microbolometer, the preparation method comprising the following steps:

[0008] Step S1, coating a thermosetting polyimide film on a wafer with a first-layer microbolometer structure in sequence, and thermosetting to obtain a wafer with a thermosetting polyimide second sacrificial layer;

[0009] Step S2, processing the wafer with the thermosetting polyimide second sacrificial layer by using a photolithography etching process, and transferring a pattern of the second sacrificial layer support hole to the wafer after the etching step of the photolithography etching process is completed;

[0010] Step S3, processing the wafer by using a wet stripping step of the photolithography etching process to remove the photoresist and etching byproducts remaining in the etching step;

[0011] Step S4, depositing a second-layer optical absorption structure by using a photolithography etching combined with a deposition process on the wafer with the second sacrificial layer support hole in sequence, preparing a PAD electrode, dicing and releasing, and packaging to obtain a double-layer microbolometer;

[0012] In step S1, the temperature of the thermosetting is 220-280℃;

[0013] In step S3, the stripping solution used in the wet stripping step comprises NMP stripping solution.

[0014] In step S1, the temperature of the thermosetting is 250℃;

[0015] Preferably, in step S3, the stripping solution used in the wet stripping step further comprises a combined stripping solution of NMP stripping solution and EKC stripping solution.

[0016] Preferably, the EKC stripping solution in the combined stripping solution used in the wet stripping step is selected from EKC830 stripping solution or / and EKC270 stripping solution.

[0017] Preferably, in step S3, the combined stripping solution used in the wet stripping step comprises 85-95 parts by volume of NMP stripping solution and 5-15 parts by volume of EKC stripping solution.

[0018] Preferably, in step S3, the combined stripping solution used in the wet stripping step comprises 90 parts by volume of NMP stripping solution and 10 parts by volume of EKC830 stripping solution.

[0019] Preferably, in step S3, the process of processing the wafer by using the wet stripping step comprises immersing the wafer in the combined stripping solution of NMP stripping solution and EKC stripping solution in sequence and stripping by using NMP stripping solution.

[0020] Preferably, the soaking process comprises soaking the wafer at a temperature of 65-80℃ for 20-50min using a combination of NMP and EKC stripping solutions.

[0021] The stripping process comprises blowing NMP stripping solution at a flow rate of 100-500mL / min onto the wafer after the peeling soaking process for 2-4min using N2 at a flow rate of 60-70L / min.

[0022] Preferably, the post-processing process of the wet stripping step comprises IPA rinsing for 15-60s, deionized water rinsing for 20-60s, and nitrogen blowing dry.

[0023] Preferably, in step S1, the thickness of the thermally cured polyimide film is 10000-25000A, and the thermally curing time is 60min-150min.

[0024] Preferably, the preparation of the wafer with the first layer of microbolometer structure in step S1 comprises using photolithography combined with deposition process to treat the wafer with the completely cured thermally cured polyimide sacrificial layer to complete the pattern transfer of the pixel structure, thereby obtaining the wafer with the first layer of microbolometer structure, which is an integrated readout circuit wafer.

[0025] Preferably, in steps S1 and S2, the photolithography machine used in the photolithography process is SF120, and the photoresist is AZ701 photoresist, AR80 photoresist or SPR220 photoresist.

[0026] In the photolithography process of steps S2 and S4, the Lam 2300 dielectric etching machine is used in the etching step, the pressure is 4mtorr, the source power is 1000W, the bias power is 150W, the CF4 flow rate is 40-80sccm, the O2 flow rate is 5-15sccm, and the He flow rate is 20-100sccm.

[0027] In step S4, the deposition method used in the deposition step of the photolithography process is CVD, PVD or ALD.

[0028] The stripping solution used in the stripping step is selected from NMP stripping solution and / or EKC stripping solution.

[0029] In step S4, the scribing and releasing is performed using the L3510 device, the temperature is 160℃, the power is 900W, the gas is a mixture of 1200sccm O2 and 21sccm H2N2, and the time is 50min.

[0030] The second aspect of the present application provides a thermal imaging detector comprising a double-layer microbolometer prepared by the preparation method of the first aspect.

[0031] The third aspect of the application provides the application of the double-layer microbolometer prepared by the preparation method of the first aspect in the security and protection field.

[0032] Compared with the prior art, the preparation method of the double-layer microbolometer provided by the application has at least the following beneficial effects:

[0033] 1. The preparation method of the double-layer microbolometer provided by the application is suitable for low-temperature curing

[0034] (250 DEG C.) of the second sacrificial layer of the thermosetting polyimide, by using a neutral stripping liquid with very weak acidity and alkalinity in the wet stripping process, it is difficult to hydrolyze the imide bond (-CO-N-CO-) of the thermosetting polyimide, so that the subsequent deposited optical absorption structure has enhanced absorption capacity for infrared energy, and the performance of the microbolometer is improved.

[0035] 2. The preparation method of the double-layer microbolometer provided by the application combines the stripping effect of the EKC stripping liquid

[0036] and the advantage that the NMP stripping liquid does not dissolve and corrode the second sacrificial layer of the thermosetting polyimide with low-temperature curing (250 DEG C.), so as to ensure that there is no residual photoresist in the aperture, and the performance of the microbolometer is further improved.

[0037] 3. Since the price of the NMP stripping liquid is much lower than that of the EKC stripping liquid, the preparation method of the double-layer microbolometer provided by the application uses the NMP stripping liquid to replace part of the EKC stripping liquid, which is conducive to reducing the production cost of enterprises and improving the efficiency.

[0038] BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 The schematic diagram of the first layer microbolometer structure in the double-layer microbolometer prepared in the embodiment 1 of the application;

[0041] Figure 2 The schematic diagram of the double-layer microbolometer prepared in the embodiment 1 of the application, wherein the A diagram is a schematic diagram of the overall structure, the B diagram is a schematic diagram of the second layer optical absorption structure, and the C diagram is a schematic diagram of the second layer optical absorption structure;

[0042] ​Figure 3 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 1 of the present application before removal of photoresist and etch byproducts remaining from the etching step;

[0043] Figure 4 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 1 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0044] Figure 5 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 2 of the present application before removal of photoresist and etch byproducts remaining from the etching step;

[0045] Figure 6 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 2 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0046] Figure 7 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 3 of the present application before removal of photoresist and etch byproducts remaining from the etching step;

[0047] Figure 8 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 3 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0048] Figure 9 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 4 of the present application before removal of photoresist and etch byproducts remaining from the etching step;

[0049] Figure 10 Test results using a film thickness meter and a 3D profilometer for the thermally cured polyimide second sacrificial layer prepared for Example 4 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0050] Figure 11 Pore mouth topography of the second sacrificial layer support hole for the thermally cured polyimide second sacrificial layer prepared for Example 1 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0051] Figure 12 Cross-sectional electron micrograph of the second sacrificial layer for the thermally cured polyimide second sacrificial layer prepared for Example 1 of the present application after removal of photoresist and etch byproducts remaining from the etching step;

[0052] Figure 13 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 3 of the present application after removing photoresist and etching by-products left over from the etching step;

[0053] Figure 14 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 5 of the present application after removing photoresist and etching by-products left over from the etching step;

[0054] Figure 15 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 6 of the present application after removing photoresist and etching by-products left over from the etching step;

[0055] Figure 16 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 7 of the present application after removing photoresist and etching by-products left over from the etching step;

[0056] Figure 17 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 8 of the present application after removing photoresist and etching by-products left over from the etching step;

[0057] Figure 18 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 9 of the present application after removing photoresist and etching by-products left over from the etching step;

[0058] Figure 19 Cross-sectional SEM image of the thermally cured polyimide second sacrificial layer prepared in Example 5 of the present application after removing photoresist and etching by-products left over from the etching step, and the aperture morphology of the second sacrificial layer support hole;

[0059] Figure 20 OM image of the thermally cured polyimide second sacrificial layer prepared in Example 5 of the present application after removing photoresist and etching by-products left over from the etching step and after the scribe release;

[0060] Figures 1-2 In the figure, the reference signs are as follows: 1-wafer substrate integrated with readout circuit, 2-thermally cured polyimide first sacrificial layer, 3-silicon nitride support layer, 4-vanadium oxide heat-sensitive layer, 5-titanium conductive layer, 6-silicon nitride passivation layer, 7-thermally cured polyimide second sacrificial layer, 8-second layer optical absorption structure. DETAILED DESCRIPTION

[0061] The present application provides a preparation method and application of a double-layer microbolometer, which is used to solve the technical problem that the preparation process of the existing microbolometer easily corrodes and dissolves the thermally cured polyimide sacrificial layer, resulting in the performance decline of the prepared microbolometer.

[0062] The technical solutions of the present application will be described clearly and completely below in conjunction with the drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0063] In view of the fact that the wet stripping solution used in the wet stripping step of the preparation process of the double-layer microbolometer is easy to corrode and dissolve the thermosetting polyimide sacrificial layer, resulting in the deviation of the cavity of the subsequently deposited optical absorption structure from the design value, the absorption capacity of infrared light decreases, and the performance of the microbolometer is reduced. The present application provides a preparation method of a double-layer microbolometer. The preparation method first prepares a first layer of microbolometer structure on a wafer integrated with a readout circuit. Then, a thermosetting polyimide film is coated and thermosetted to obtain a wafer with a second thermosetting polyimide sacrificial layer. Next, the photolithography and etching process is used to transfer the pattern of the second sacrificial layer support hole to the wafer through the steps of glue coating, pre-baking, exposure, development, post-baking and etching. Then, the wafer is treated by a wet stripping step to remove the photoresist and etching by-products remaining on the wafer after the etching step. Subsequently, the photolithography and etching combined with the deposition process are used to complete the pattern transfer of the second layer of optical absorption structure. Next, the PAD electrode is prepared, and the wafer is scribed and released to form a suspended thermal isolation structure and packaged to obtain a double-layer microbolometer.

[0064] The application provides a preparation method of a double-layer microbolometer, in which the preparation of the first-layer microbolometer structure is first coating a thermosetting polyimide film on a wafer integrated with a readout circuit and completely thermosetting, then processing the wafer with the completely solidified thermosetting polyimide sacrificial layer by using a photolithography etching combined with a deposition process to complete the pattern transfer of the pixel structure and obtain the wafer with the first-layer microbolometer structure. The thermosetting temperature of the thermosetting polyimide film coated after the preparation of the first-layer microbolometer structure is 220-280 DEG C, which is in the low-temperature range of the thermosetting polyimide solidification temperature range and is difficult to be completely solidified. Therefore, the thermosetting polyimide as the second sacrificial layer is a low-temperature insufficiently solidified polyimide, which can provide basic mechanical support but is prone to hydrolysis of the imide bond (-CO-N-CO-) in the low-temperature insufficiently solidified polyimide due to the alkaline nature of the traditional EKC830 / EKC270 EKC stripping liquid with a pH value of 10-12, especially for the low-temperature insufficiently solidified polyimide, which leads to the thickness loss, uniformity deterioration and surface roughening of the thermosetting polyimide as the sacrificial layer, the deviation of the cavity of the subsequently deposited optical absorption structure from the design value, the decline of the absorption capacity of infrared light, the decline of the performance of the microbolometer, and the use of the NMP stripping liquid which is a neutral stripping liquid with extremely weak acidity and alkalinity to remove the photoresist and etching by-products remaining after the etching step of the photolithography etching process, which does not hydrolyze the imide bond (-CO-N-CO-) of the thermosetting polyimide and does not cause chemical corrosion to cause the thickness loss, uniformity deterioration and surface roughening of the thermosetting polyimide as the second sacrificial layer, which is beneficial to the maintenance of the cavity of the subsequently deposited optical absorption structure at the design value, the non-damage of the microbolometer structure, the enhancement of the absorption capacity of infrared energy, the better performance of the prepared microbolometer, and the overcoming of the defects of the existing microbolometer preparation process, such as the corrosion and dissolution of the thermosetting polyimide sacrificial layer and the decline of the performance of the prepared microbolometer.

[0065] As a preferred technical solution, the application provides a preparation method of a double-layer microbolometer, wherein a combined stripping solution is used for pre-soaking in a wet stripping process, and the combined stripping solution is a combination of NMP stripping solution and EKC stripping solution; because the NMP stripping solution has a general process window, it is easy to leave a small amount of residual glue at the orifice of the thermosetting polyimide serving as a second sacrificial layer, and the application further improves the technical solution, that is, by using the combined stripping solution of the NMP stripping solution and the EKC stripping solution for pre-soaking, the photoresist and etching byproducts remaining in the etching step are softened, and then using pure NMP stripping solution for stripping ensures that there is no small amount of residual glue at the orifice of the thermosetting polyimide, the deposited optical absorption structure is closer to the design value, and the performance of the microbolometer is improved.

[0066] As a preferred technical solution, the application provides a preparation method of a double-layer microbolometer, wherein a combined stripping solution is used for pre-soaking in a wet stripping process, and the combined stripping solution is a combination of NMP stripping solution and EKC stripping solution; because the NMP stripping solution has a general process window, it is easy to leave a small amount of residual glue at the orifice of the thermosetting polyimide serving as a second sacrificial layer, and the application further improves the technical solution, that is, by using the combined stripping solution of the NMP stripping solution and the EKC stripping solution for pre-soaking, the photoresist and etching byproducts remaining in the etching step are softened, and then using pure NMP stripping solution for stripping ensures that there is no small amount of residual glue at the orifice of the thermosetting polyimide, the deposited optical absorption structure is closer to the design value, and the performance of the microbolometer is improved.

[0067] The preparation method and application of a double-layer microbolometer provided by the application will be described in detail below with reference to examples and experimental examples.

[0068] Example 1

[0069] The application provides a preparation method of a double-layer microbolometer, and the structure of the prepared double-layer microbolometer is as shown in Figures 1-2 The preparation method includes the steps of preparing a first-layer microbolometer structure, preparing a thermosetting polyimide second sacrificial layer, photoetching, and preparing a double-layer microbolometer.

[0070] The step of preparing the first-layer microbolometer structure includes the following steps: first, coating a thermosetting polyimide film (DuPont PI2610) on a wafer substrate of an integrated readout circuit and completely heat-curing the thermosetting polyimide film as a thermosetting polyimide first sacrificial layer; then, using photoetching and deposition process to process the wafer with the completely cured thermosetting polyimide sacrificial layer, to complete the pixel structure including a silicon nitride support layer, a vanadium oxide thermal sensitive layer, a titanium conductive layer, and a silicon nitride passivation layer, and to obtain a wafer with a first-layer microbolometer structure, and the structure is as shown in Figure 1 .

[0071] The step of preparing the second sacrificial layer of thermally cured polyimide includes: coating the second layer of thermally cured polyimide film (DuPont PI2610) onto the wafer with the first layer of microbolometer structure, and placing in a furnace tube for curing after spin coating, with a curing temperature of 250°C and a curing time of 2h, to obtain a wafer with the second sacrificial layer of thermally cured polyimide.

[0072] The step of photolithography includes: first using a photolithography machine SF120 and photoresist AZ701 to perform photolithography on the wafer with the second sacrificial layer of thermally cured polyimide, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, with an etching pressure of 4mtorr, a bias power of 150W, a CF4flow rate of 60sccm, an O2flow rate of 10sccm, and a He flow rate of 60sccm, and transferring the pattern of the second sacrificial layer support hole to the wafer after etching; then using a KS-S200-6ST full-automatic wet stripping machine to remove the photoresist and etching by-products remaining after the etching step, with the stripping process being first immersed in NMP stripping liquid (Jianghua Micro) for 40min at a temperature of 70°C, and then peeled off using the same NMP stripping liquid (Jianghua Micro), with N2blowing at a flow rate of 70L / min and a stripping liquid flow rate of 300mL / min, and a peeling time of 3min, followed by the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing for drying.

[0073] The step of preparing the double-layer microbolometer includes: after removing the photoresist and etching by-products remaining after the etching step in the second sacrificial layer support hole, depositing the second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photolithography combined with CVD / PVD process, with the second layer of optical absorption structure being provided with a square hole required for scribe release, and the structure being as shown in Figure 2 Next, the PAD electrode preparation is completed, scribe release is performed, a suspended thermal isolation structure is formed, and the double-layer microbolometer is obtained after packaging.

[0074] Example 2

[0075] The present embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of Example 1, and the preparation method includes the steps of preparing the first layer of microbolometer structure, preparing the second sacrificial layer of thermally cured polyimide, photolithography, and preparing the double-layer microbolometer.

[0076] The step of preparing the first layer microbolometer structure includes: firstly coating a thermosetting polyimide film (DuPont PI2610) on the wafer substrate of the integrated readout circuit and completely heat curing as a first thermosetting polyimide sacrificial layer, and then processing the wafer with the completely cured thermosetting polyimide sacrificial layer by using photolithography etching combined with a deposition process to complete the patterned transfer of the pixel structure including a silicon nitride support layer, a vanadium oxide heat-sensitive layer, a titanium conductive layer, and a silicon nitride passivation layer, thereby obtaining a wafer with the first layer microbolometer structure.

[0077] The step of preparing the second thermosetting polyimide sacrificial layer includes: coating a second layer of thermosetting polyimide film (DuPont PI2610) onto the wafer with the first layer microbolometer structure, and after spin coating, placing it in a furnace tube for curing at a temperature of 350°C for 2 hours, thereby obtaining a wafer with a second thermosetting polyimide sacrificial layer.

[0078] The step of photolithography etching includes: firstly using a photoetching machine SF120 and photoresist AZ701 to perform photolithography etching on the wafer with the second thermosetting polyimide sacrificial layer, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer at a pressure of 4mtorr, a source power of 1000W, a bias power of 150W, a CF4flow rate of 60sccm, an O2flow rate of 10sccm, and a He flow rate of 60sccm, and after etching, transferring the pattern of the second sacrificial layer support hole to the wafer; then using a KS-S200-6ST full-automatic wet stripping machine to strip the photoresist and etching by-products remaining after the etching step, the stripping process is as follows: firstly immersing in NMP stripping liquid (Jianghua Micro) for 40min at a temperature of 70°C, and then peeling off using the same NMP stripping liquid (Jianghua Micro), blowing out with N2, an N2flow rate of 70L / min, a stripping liquid flow rate of 300mL / min, a peeling time of 3min, and then sequentially performing the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0079] The step of preparing the double-layer microbolometer includes: after removing the photoresist and etching by-products remaining after the etching step in the second sacrificial layer support hole, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by using photolithography etching combined with CVD / PVD process, and the second layer of optical absorption structure is provided with a square hole required for scribe release; then completing the preparation of the PAD electrode, releasing the scribe, and forming a suspended thermal isolation structure, thereby obtaining a double-layer microbolometer.

[0080] Example 3

[0081] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of the embodiment 1. The preparation method comprises the steps of preparing a first-layer microbolometer structure, preparing a heat-cured polyimide second sacrificial layer, photoetching, and preparing a double-layer microbolometer.

[0082] The step of preparing the first-layer microbolometer structure comprises the following steps: coating a heat-cured polyimide film (DuPont PI2610) on a wafer substrate of an integrated readout circuit and completely heat-curing the heat-cured polyimide film as a heat-cured polyimide first sacrificial layer, and processing the wafer with the completely cured heat-cured polyimide sacrificial layer by using a photoetching and deposition process to complete the patterned transfer of a pixel structure comprising a silicon nitride support layer, a vanadium oxide heat-sensitive layer, a titanium conductive layer and a silicon nitride passivation layer, so as to obtain a wafer with the first-layer microbolometer structure.

[0083] The step of preparing the heat-cured polyimide second sacrificial layer comprises the following steps: coating a second-layer heat-cured polyimide film (DuPont PI2610) on the wafer with the first-layer microbolometer structure, and placing the wafer in a furnace tube for curing after spin coating, wherein the curing temperature is 250 DEG C and the curing time is 2h, so as to obtain a wafer with the heat-cured polyimide second sacrificial layer.

[0084] The step of photoetching comprises the following steps: firstly, using a photoetching machine SF120 and a photoresist AZ701 to perform photoetching on the wafer with the heat-cured polyimide second sacrificial layer, after the steps of coating, pre-baking, exposure, development and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, wherein the etching pressure is 4mtorr, the source power is 1000W, the bias power is 150W, the CF4 flow rate is 60sccm, the O2 flow rate is 10sccm, and the He flow rate is 60sccm, and the pattern of the second sacrificial layer support hole is transferred to the wafer after etching; and then using a KS-S200-6ST full-automatic wet stripping machine to strip the photoresist and etching by-products remaining in the etching step, wherein the stripping process comprises the following steps: firstly, immersing in EKC830 stripping liquid (DuPont, USA) for 40min at a temperature of 70 DEG C, and then peeling off by using EKC270 stripping liquid (DuPont, USA) and blowing out by using N2, wherein the N2 flow rate is 70L / min, the stripping liquid flow rate is 300mL / min, the peeling-off time is 3min, and the following post-processing steps are sequentially performed, i.e., IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0085] The steps of preparing the double-layer microbolometer include: after removing the photoresist and etching by-products remaining in the etching step of the second sacrificial layer support hole, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photolithography etching combined with CVD / PVD process, the second layer of optical absorption structure is provided with a square hole required for scribe release; then, after completing the preparation of the PAD electrode and scribe release, a suspended thermal isolation structure is formed, and the double-layer microbolometer is obtained after packaging.

[0086] Embodiment 4

[0087] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of embodiment 3, and the preparation method comprises the steps of preparing a first-layer microbolometer structure, preparing a thermosetting polyimide second sacrificial layer, photolithography etching, and preparing a double-layer microbolometer.

[0088] The step of preparing the first-layer microbolometer structure comprises the following steps: first, coating a thermosetting polyimide film (DuPont PI2610) on a wafer substrate of an integrated readout circuit and completely thermosetting to serve as a thermosetting polyimide first sacrificial layer, and then processing the wafer with the completely cured thermosetting polyimide sacrificial layer by photolithography etching combined with a deposition process to complete the patterned transfer of a pixel structure including a silicon nitride support layer, a vanadium oxide thermal sensitive layer, a titanium conductive layer and a silicon nitride passivation layer, so as to obtain a wafer with a first-layer microbolometer structure.

[0089] The step of preparing the thermosetting polyimide second sacrificial layer comprises the following steps: coating a second layer of thermosetting polyimide film (DuPont PI2610) on the wafer with the first-layer microbolometer structure, and after spin coating, placing the wafer in a furnace tube for curing, the curing temperature is 350 DEG C, and the curing time is 2 h, so as to obtain a wafer with a thermosetting polyimide second sacrificial layer.

[0090] The photoetching step includes: firstly, using a photoetching machine SF120 and photoresist AZ701 to photoetch a wafer with a thermosetting polyimide second sacrificial layer, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 medium etching machine to etch the area of the second sacrificial layer support hole on the wafer, the etching pressure is 4mtorr, the source power is 1000W, the bias power is 150W, the CF4 flow is 60sccm, the O2 flow is 10sccm, the He flow is 60sccm, and the pattern of the second sacrificial layer support hole is transferred to the wafer after etching; then using KS-S200-6ST full-automatic wet stripping machine to strip, removing the photoresist and etching by-products remaining in the etching step, the stripping process is firstly soaked in EKC830 stripping solution (DuPont, USA) for 40min, the soaking temperature is 70℃, then stripped using EKC270 stripping solution (DuPont, USA), blowing out with N2, the N2 flow is 70L / min, the stripping solution flow is 300mL / min, the stripping time is 3min, and then sequentially performing IPA rinsing for 35S, deionized water rinsing for 40S, nitrogen blowing drying, and other post-processing steps.

[0091] The step of preparing a double-layer microbolometer includes: after removing the photoresist and etching by-products remaining in the second sacrificial layer support hole etching step, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photoetching combined with CVD / PVD process, the second layer of optical absorption structure is provided with a square hole required for scribe release; after completing the preparation of the PAD electrode, the scribe release forms a suspended thermal isolation structure, and the packaging obtains a double-layer microbolometer.

[0092] Example 5

[0093] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of the embodiment 1, the preparation method includes the steps of preparing a first layer microbolometer structure, preparing a thermosetting polyimide second sacrificial layer, photoetching, and preparing a double-layer microbolometer.

[0094] The step of preparing a first layer microbolometer structure includes: firstly, coating a thermosetting polyimide film (DuPont PI2610) on a wafer substrate integrated with a readout circuit and completely thermosetting as a thermosetting polyimide first sacrificial layer, then using photoetching combined with deposition process to process the wafer with the completely cured thermosetting polyimide sacrificial layer, to complete the pattern transfer of the pixel structure including a silicon nitride support layer, a vanadium oxide thermal sensitive layer, a titanium conductive layer, and a silicon nitride passivation layer, to obtain a wafer with a first layer microbolometer structure.

[0095] The step of preparing the second sacrificial layer of thermally cured polyimide includes: coating the second layer of thermally cured polyimide film (DuPont PI2610) onto the wafer with the first layer of microbolometer structure, and placing in a furnace tube for curing after spin coating, with a curing temperature of 250°C and a curing time of 2h, to obtain a wafer with the second sacrificial layer of thermally cured polyimide.

[0096] The step of photolithography includes: first using a photolithography machine SF120 and photoresist AZ701 to perform photolithography on the wafer with the second sacrificial layer of thermally cured polyimide, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, with an etching pressure of 4mtorr, a source power of 1000W, a bias power of 150W, a CF4flow rate of 60sccm, an O2flow rate of 10sccm, and a He flow rate of 60sccm, and transferring the pattern of the second sacrificial layer support hole to the wafer after etching; and then using a KS-S200-6ST full-automatic wet stripping machine to remove the photoresist and etching by-products remaining after the etching step, with the stripping process being first immersed in a combined stripping solution (NMP:EKC830 in a volume ratio of 90:10) for 40min at an immersion temperature of 70°C, and then peeled off using the same NMP stripping solution (Jianghua Micro) by blowing out with N2, with an N2flow rate of 70L / min, a stripping solution flow rate of 300mL / min, a peeling time of 3min, and subsequent post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0097] The step of preparing the double-layer microbolometer includes: after removing the photoresist and etching by-products remaining after the etching step in the second sacrificial layer support hole, depositing the second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photolithography combined with CVD / PVD process, and providing a square hole required for scribe release for the second layer of optical absorption structure; and then forming a suspended thermal isolation structure after completing the preparation of the PAD electrode and scribe release, and packaging to obtain the double-layer microbolometer.

[0098] Example 6

[0099] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of Example 1, and the preparation method includes the steps of preparing the first layer of microbolometer structure, preparing the second sacrificial layer of thermally cured polyimide, photolithography, and preparing the double-layer microbolometer.

[0100] The step of preparing the first layer microbolometer structure includes: firstly coating a thermosetting polyimide film (DuPont PI2610) on the wafer substrate of the integrated readout circuit and completely heat-curing as a first thermosetting polyimide sacrificial layer, and then processing the wafer with the completely cured thermosetting polyimide sacrificial layer by using photolithography etching combined with a deposition process to complete the patterned transfer of the pixel structure including a silicon nitride support layer, a vanadium oxide heat-sensitive layer, a titanium conductive layer, and a silicon nitride passivation layer, thereby obtaining a wafer with the first layer microbolometer structure.

[0101] The step of preparing the second thermosetting polyimide sacrificial layer includes: coating a second layer of thermosetting polyimide film (DuPont PI2610) on the wafer with the first layer microbolometer structure, and then placing it in a furnace tube for curing after spin coating, with a curing temperature of 250°C and a curing time of 2h, thereby obtaining a wafer with a second thermosetting polyimide sacrificial layer.

[0102] The step of photolithography etching includes: firstly using a photoetching machine SF120 and photoresist AZ701 to perform photolithography etching on the wafer with the second thermosetting polyimide sacrificial layer, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, with an etching pressure of 4mtorr, a source power of 1000W, a bias power of 150W, a CF4flow rate of 60sccm, an O2flow rate of 10sccm, and a He flow rate of 60sccm, and then transferring the pattern of the second sacrificial layer support hole to the wafer after etching; and then using a KS-S200-6ST full-automatic wet stripping machine to remove the photoresist and etching by-products remaining after the etching step, with the stripping process being: firstly immersing for 40min in a combined stripping solution (NMP:EKC830 in a volume ratio of 70:30) at an immersion temperature of 70°C, and then peeling off using the same NMP stripping solution (Jianghua Micro) at a N2flow rate of 70L / min and a stripping solution flow rate of 300mL / min for 3min, followed by the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0103] The step of preparing the double-layer microbolometer includes: after removing the photoresist and etching by-products remaining after the etching step in the second sacrificial layer support hole, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by using photolithography etching combined with CVD / PVD process, and providing a square hole for scribe release in the second layer of optical absorption structure; and then forming a suspended thermal isolation structure after completing the preparation of the PAD electrode and scribe release, and packaging to obtain the double-layer microbolometer.

[0104] Example 7

[0105] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of the embodiment 1. The preparation method comprises the steps of preparing a first-layer microbolometer structure, preparing a heat-cured polyimide second sacrificial layer, photolithography and preparing the double-layer microbolometer.

[0106] The step of preparing the first-layer microbolometer structure comprises the following steps: firstly, coating a heat-cured polyimide film (DuPont PI2610) on a wafer substrate of an integrated readout circuit and completely heat-curing the heat-cured polyimide film as a heat-cured polyimide first sacrificial layer; secondly, processing the wafer with the completely cured heat-cured polyimide sacrificial layer by using a photolithography and deposition process, to complete the patterned transfer of a pixel structure comprising a silicon nitride support layer, a vanadium oxide heat-sensitive layer, a titanium conductive layer and a silicon nitride passivation layer, and to obtain a wafer with the first-layer microbolometer structure.

[0107] The step of preparing the heat-cured polyimide second sacrificial layer comprises the following steps: coating a second-layer heat-cured polyimide film (DuPont PI2610) on the wafer with the first-layer microbolometer structure, and then placing the wafer in a furnace tube for curing after spin coating, with a curing temperature of 250 DEG C and a curing time of 2 h, to obtain a wafer with the heat-cured polyimide second sacrificial layer.

[0108] The step of photolithography comprises the following steps: firstly, using a photolithography machine SF120 and a photoresist AZ701 to perform photolithography on the wafer with the heat-cured polyimide second sacrificial layer, after the steps of coating, pre-baking, exposure, development and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, with an etching pressure of 4mtorr, a source power of 1000W, a bias power of 150W, a CF4 flow rate of 60sccm, an O2 flow rate of 10sccm and a He flow rate of 60sccm, and then transferring the pattern of the second sacrificial layer support hole to the wafer after etching; and then using a KS-S200-6ST full-automatic wet stripping machine to strip the photoresist and etching by-products remaining after the etching step, with the stripping process being: firstly, immersing in a combined stripping liquid (NMP:EKC830 with a volume ratio of 50:50) for 40 min at an immersion temperature of 70 DEG C, and then peeling off using the same NMP stripping liquid (Jianghua Micro), with N2 blowing out at a flow rate of 70 L / min, a stripping liquid flow rate of 300 mL / min and a peeling time of 3 min, and then sequentially performing the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S and nitrogen blowing dry.

[0109] The steps of preparing the double-layer microbolometer include: after removing the photoresist and etching by-products remaining in the etching step of the second sacrificial layer support hole, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photolithography etching combined with CVD / PVD process, the second layer of optical absorption structure is provided with a square hole required for scribe release; then, after completing the preparation of the PAD electrode and scribe release, a suspended thermal isolation structure is formed, and the double-layer microbolometer is obtained after packaging.

[0110] Embodiment 8

[0111] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of embodiment 1, and the preparation method comprises the steps of preparing a first-layer microbolometer structure, preparing a thermosetting polyimide second sacrificial layer, photolithography etching, and preparing a double-layer microbolometer.

[0112] The step of preparing the first-layer microbolometer structure comprises the following steps: first, coating a thermosetting polyimide film (DuPont PI2610) on a wafer substrate of an integrated readout circuit and completely thermosetting to serve as a thermosetting polyimide first sacrificial layer, and then processing the wafer with the completely cured thermosetting polyimide sacrificial layer by photolithography etching combined with a deposition process to complete the patterned transfer of a pixel structure including a silicon nitride support layer, a vanadium oxide thermal sensitive layer, a titanium conductive layer and a silicon nitride passivation layer, so as to obtain a wafer with a first-layer microbolometer structure.

[0113] The step of preparing the thermosetting polyimide second sacrificial layer comprises the following steps: coating a second layer of thermosetting polyimide film (DuPont PI2610) on the wafer with the first-layer microbolometer structure, and after spin coating, placing the wafer in a furnace tube for curing, with a curing temperature of 250 DEG C and a curing time of 2 h, so as to obtain a wafer with a thermosetting polyimide second sacrificial layer.

[0114] The photoetching step includes: firstly, using a photoetching machine SF120 and photoresist AZ701 to photoetch a wafer with a thermosetting polyimide second sacrificial layer, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 medium etching machine to etch the area of the second sacrificial layer support hole on the wafer, the etching pressure is 4mtorr, the source power is 1000W, the bias power is 150W, the CF4 flow is 60sccm, the O2 flow is 10sccm, the He flow is 60sccm, and the pattern of the second sacrificial layer support hole is transferred to the wafer after etching; then using a KS-S200-6ST full-automatic wet stripping machine to strip, remove the photoresist and etching by-products remaining in the etching step, the stripping process is to first soak in a combined stripping solution (NMP:EKC830 in a volume ratio of 30:70) for 40min, the soaking temperature is 70℃, then use the same NMP stripping solution (Jianghua Micro) to strip, blow out with N2, the N2 flow is 70L / min, the stripping solution flow is 300mL / min, the stripping time is 3min, and then sequentially perform the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0115] The step of preparing a double-layer microbolometer includes: after removing the photoresist and etching by-products remaining in the second sacrificial layer support hole etching step, depositing a second layer of optical absorption structure silicon nitride / titanium / silicon nitride by photoetching combined with CVD / PVD process, the second layer of optical absorption structure is provided with a square hole required for scribe release; after completing the preparation of the PAD electrode, the scribe release forms a suspended thermal isolation structure, and the packaging obtains a double-layer microbolometer.

[0116] Embodiment 9

[0117] The embodiment provides a preparation method of a double-layer microbolometer, which is a comparative example of embodiment 1, and the preparation method comprises the steps of preparing a first-layer microbolometer structure, preparing a thermosetting polyimide second sacrificial layer, photoetching, and preparing a double-layer microbolometer.

[0118] The step of preparing a first-layer microbolometer structure comprises the following steps: firstly, coating a thermosetting polyimide film (DuPont PI2610) on a wafer substrate integrated with a readout circuit and completely thermosetting as a thermosetting polyimide first sacrificial layer, and then adopting photoetching combined with a deposition process to process the wafer with the completely cured thermosetting polyimide sacrificial layer, to complete the pattern transfer of the pixel structure including a silicon nitride support layer, a vanadium oxide thermal sensitive layer, a titanium conductive layer, and a silicon nitride passivation layer, and obtain a wafer with a first-layer microbolometer structure.

[0119] The step of preparing the second sacrificial layer of thermally cured polyimide includes: coating the second layer of thermally cured polyimide film (DuPont PI2610) onto the wafer with the first layer of microbolometer structure, and placing it in a furnace tube for curing after spin coating, with a curing temperature of 250°C and a curing time of 2h, to obtain a wafer with a second sacrificial layer of thermally cured polyimide.

[0120] The step of photolithography includes: first using a photolithography machine SF120 and photoresist AZ701 to perform photolithography on the wafer with the second sacrificial layer of thermally cured polyimide, after the steps of coating, pre-baking, exposure, development, and post-baking, using a Lam 2300 dielectric etching machine to etch the area of the second sacrificial layer support hole on the wafer, with an etching pressure of 4mtorr, a source power of 1000W, a bias power of 150W, a CF4flow rate of 60sccm, an O2flow rate of 10sccm, and a He flow rate of 60sccm, and transferring the pattern of the second sacrificial layer support hole to the wafer after etching; then using a KS-S200-6ST full-automatic wet stripping machine to remove the photoresist and etching by-products remaining after the etching step, with the stripping process being first immersed in a combined stripping solution (NMP:EKC830 with a volume ratio of 10:90) for 40min at a temperature of 70°C, and then peeled off using the same NMP stripping solution (Jianghua Micro) with N2blowing, an N2flow rate of 70L / min, a stripping solution flow rate of 300mL / min, and a peeling time of 3min, followed by the post-processing steps of IPA rinsing for 35S, deionized water rinsing for 40S, and nitrogen blowing dry.

[0121] The step of preparing the double-layer microbolometer includes: after removing the photoresist and etching by-products remaining after the etching step in the second sacrificial layer support hole, depositing the second layer of optical absorption structure silicon nitride / titanium / silicon nitride using photolithography combined with CVD / PVD process, and providing a square hole for scribe release in the second layer of optical absorption structure; then completing the preparation of the PAD electrode and forming the suspended thermal isolation structure after scribe release, and packaging to obtain the double-layer microbolometer.

[0122] Experimental Example 1

[0123] This experimental example tests the double-layer microbolometer prepared in the embodiments, including testing the thickness, uniformity, and roughness of the second sacrificial layer of thermally cured polyimide provided in Examples 1-4 before and after removing the photoresist and etching by-products remaining after the etching step using a film thickness meter and a 3D profiler.

[0124] Among them, the thickness and uniformity test results of the second sacrificial layer of thermally cured polyimide in Examples 1-4 before and after removing the photoresist and etching by-products remaining after the etching step are as shown in Figures 3-10 Figures 7-8 / Figures 9-10 ​It can be seen that the preparation method of the double-layer microbolometer provided in Embodiment 3-4, after the second sacrificial layer of thermosetting polyimide is cured at 250°C / 350°C, in the stripping step for removing the photoresist and etching by-products remaining in the etching step, EKC830 stripping liquid / EKC270 stripping liquid is used for stripping. Because EKC830 stripping liquid / EKC270 stripping liquid is relatively strong in alkalinity, after stripping, the thickness of the hole thermosetting polyimide second sacrificial layer decreases, especially the thermosetting polyimide second sacrificial layer cured at a low temperature of 250°C, the thickness and uniformity std of the second sacrificial layer before and after stripping decrease significantly, and the roughness Ra also decreases from 0.49 nm before stripping to 0.67 nm, the roughness is significantly worse, and from the 3D profile map, it can be seen that the concave-convex phenomenon left after the liquid erosion, which shows that for the low-temperature cured thermosetting polyimide second sacrificial layer, using EKC stripping liquid will corrode and dissolve the imide bond (-CO-N-CO-) of the thermosetting polyimide. The decrease of the thickness, uniformity and roughness of the thermosetting polyimide second sacrificial layer as a mechanical support will lead to the deviation of the thickness of the air resonance cavity formed after release from the design value, thereby weakening the infrared absorption capacity; on the other hand, it will lead to poor uniformity of the second layer optical absorption structure deposition, affecting the uniformity of the detector, and thus the performance of the double-layer microbolometer as a whole will decrease, and from the Figures 3-6 It can be seen that whether the second sacrificial layer of thermosetting polyimide is cured at 250°C or 350°C, and after curing, NMP stripping liquid is used for stripping, the thickness and uniformity before and after stripping remain basically unchanged, and the roughness also remains basically unchanged. The thickness of the air resonance cavity formed after release is close to the design value, maintaining the infrared absorption capacity, and the uniformity of the second layer optical absorption structure deposition is excellent, the uniformity of the detector is improved, and the performance of the double-layer microbolometer is improved.

[0125] Experimental Example 2

[0126] After the second sacrificial layer of thermosetting polyimide provided in Embodiment 1 is removed after the etching step, the photoresist and etching by-products remaining in the etching step are analyzed by scanning electron microscopy, and it is found that although the thickness, uniformity and roughness of the second sacrificial layer of thermosetting polyimide are good, a small amount of photoresist is still left on the hole of the second sacrificial layer support hole (as shown in FIG. 3B), which will affect the uniformity of the second layer optical absorption structure deposition, and the uniformity of the detector will be affected, and the performance of the double-layer microbolometer will be affected. Figure 11EKC as the combined stripping solution in the stripping step, and then using NMP stripping solution for stripping, it is expected to combine the stripping effect of EKC and the advantage that NMP stripping solution will not dissolve and corrode the low-temperature cured (250°C) thermosetting polyimide second sacrificial layer. Further, the thermosetting polyimide second sacrificial layer provided by Example 5 was analyzed by scanning electron microscopy after removing the photoresist and etching by-products remaining in the etching step, and the results are shown in FIG. 6. It was found that there was no residual photoresist in the aperture. Further, the MEMS device provided by Example 5 after stripping was taken to an OM to observe the color difference flatness, and the results are shown in FIG. 7. It was found that the MEMS device provided by Example 5 after stripping had no color difference after release, and the structure flatness was better, so that the detection performance of the double-layer microbolometer can be further improved.

[0127] The thickness and uniformity test results of the thermosetting polyimide second sacrificial layer provided by Examples 5-9 before and after removing the photoresist and etching by-products remaining in the etching step, and the test results of Examples 1 and 3 in Experimental Example 1 are shown in Table 1, and the scanning electron microscopy images of the thermosetting polyimide second sacrificial layer provided by Examples 1, 3 and Examples 5-9 after removing the photoresist and etching by-products remaining in the etching step are shown in FIGS. 8-12. Figures 12-18 Figures 12-18 It can be seen from Table 1 and FIGS. 8-12 that when NMP:EKC830 with a volume ratio of 10:90 is used as the combined stripping solution in the stripping step, it basically has no effect on the thickness and uniformity of the thermosetting polyimide second sacrificial layer, and when NMP:EKC830 with a volume ratio of 30:90 is used as the combined stripping solution in the stripping step, it will have an adverse effect on the thickness and uniformity of the thermosetting polyimide second sacrificial layer, which shows that when NMP:EKC830 with a volume ratio of 10:90 is used as the combined stripping solution in the stripping step, and then NMP stripping solution is used for stripping, it is expected to combine the stripping effect of EKC and the advantage that NMP stripping solution will not dissolve and corrode the low-temperature cured (250°C) thermosetting polyimide second sacrificial layer. Further, the thermosetting polyimide second sacrificial layer provided by Example 5 was analyzed by scanning electron microscopy after removing the photoresist and etching by-products remaining in the etching step, and the results are shown in FIG. 6. It was found that there was no residual photoresist in the aperture. Further, the MEMS device provided by Example 5 after stripping was taken to an OM to observe the color difference flatness, and the results are shown in FIG. 7. It was found that the MEMS device provided by Example 5 after stripping had no color difference after release, and the structure flatness was better, so that the detection performance of the double-layer microbolometer can be further improved. Figure 19 Figure 20

[0128] Table 1: Thickness and uniformity test results

[0129] ​​​

[0130] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for fabricating a bilayer microbolometer, characterized by, The method comprises the following steps: Step S1, coating a heat-cured polyimide film on a wafer with a first layer of microbolometer structure, and heat-curing to obtain a wafer with a heat-cured polyimide second sacrificial layer; Step S2, processing the wafer with the heat-cured polyimide second sacrificial layer by using a photolithography etching process, and transferring a pattern of the second sacrificial layer support hole to the wafer after the etching step of the photolithography etching process is completed; Step S3, processing the wafer by using a wet stripping step of the photolithography etching process to remove the photoresist and etching by-products remaining in the etching step; Step S4, depositing a second layer of optical absorption structure on the wafer with the second sacrificial layer support hole by using a photolithography etching combined with a deposition process, preparing a PAD electrode, dicing and releasing, and packaging to obtain a double-layer microbolometer; In step S1, the temperature of the heat-curing is 220-280℃; In step S3, the wet stripping solution used in the wet stripping step comprises NMP stripping solution.

2. The method of claim 1, wherein the method further comprises, In step S3, the wet stripping solution used in the wet stripping step further comprises a combination of NMP stripping solution and EKC stripping solution.

3. The method of claim 2, wherein the method further comprises, The EKC stripping solution in the combination of the wet stripping solution is selected from EKC830 stripping solution or / and EKC270 stripping solution.

4. The method of claim 2, wherein the method further comprises, In step S3, the combination of the wet stripping solution comprises 85-95 parts by volume of NMP stripping solution and 5-15 parts by volume of EKC stripping solution.

5. The method of claim 2, wherein the method further comprises: In step S3, the process of processing the wafer by using the wet stripping step comprises immersing the wafer in a combination of NMP stripping solution and EKC stripping solution, and stripping the NMP stripping solution.

6. The method of claim 5, wherein the method further comprises: The immersion process comprises immersing the wafer in a combination of NMP stripping solution and EKC stripping solution at a temperature of 65-80℃ for 20-50min.

7. The method of claim 5, wherein the method further comprises: The stripping process comprises blowing the NMP stripping solution at a flow rate of 100-500mL / min to strip the immersed wafer by using N2 at a flow rate of 60-70L / min for 2-4min.

8. The method of claim 1, wherein the method further comprises: In step S1, the thickness of the coated heat-cured polyimide film is 10000-25000A, and the heat-curing time is 60-150min.

9. A thermal imaging detector, characterized by A double-layer microbolometer prepared by the preparation method of any one of claims 1-8.

10. Application of the double-layer microbolometer prepared by the preparation method of any one of claims 1-8 in the field of security and protection.

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