Polyimide film passive optical filter device and method of making same

Abstract

This invention provides a polyimide thin-film passive optical filter device and its fabrication method. The fabrication method includes: providing a semiconductor substrate, and sequentially forming a dielectric layer and a polyimide thin film layer on the front side of the semiconductor substrate; forming a barrier layer on the polyimide thin film layer; forming a first patterned photoresist layer on the barrier layer to obtain a photolithographic pattern of the outer contour of the thin film; sequentially etching the barrier layer, the polyimide thin film layer, and the dielectric layer based on the first patterned photoresist layer; forming a second patterned photoresist layer on the back side of the semiconductor substrate to obtain a photolithographic pattern of the inner contour of the thin film; etching the semiconductor substrate using a deep reactive ion etching process based on the second patterned photoresist layer to form an etching window; and removing the dielectric layer using a dry etching process based on the etching window to obtain the polyimide thin-film passive optical filter device. This fabrication method can effectively improve the performance of the polyimide thin film.

Description

Technical Field

[0001] This invention relates to materials science and short-wavelength science, and in particular to a polyimide thin film passive optical filter device and its preparation method, which can be applied to soft X-ray astronomy filters. Background Technology

[0002] Passive optical filters are key components in space soft X-ray detection technology, and passive filter films are crucial components within these devices. For passive filter films to be used in space soft X-ray detection, they must possess characteristics such as thin and uniform thickness, wide operating temperature range, and large usable area. Traditional polymer materials used in soft X-ray optics include polypropylene and polycarbonate, but their tensile and flexural strengths are relatively low. Polyimide, due to its excellent mechanical properties, thermal stability, chemical resistance, and dielectric properties, has been chosen as the primary support material for passive filter films. Furthermore, polyimide films can withstand irradiation doses reaching 5 × 10⁻⁶ ppm. 7 The intensity can still be maintained at 86% at Gy, which once again verifies its suitability for space exploration.

[0003] Currently used methods for preparing self-supporting polyimide films all affect the performance of polyimide, leading to a decrease in its properties. For example, the release method involves a release agent, a soluble substance grown or coated between the polyimide film and the substrate, usually an inorganic salt or surfactant. After the polyimide film formation process, the release agent is dissolved to quickly and easily obtain a self-supporting structure. However, the introduction of the release agent itself increases the surface roughness of the substrate, which in turn affects the surface roughness and uniformity of the submicron-level polyimide film. Furthermore, release agents are environmentally sensitive and can easily introduce defects into the polyimide, further degrading the surface quality of the polyimide film. Moreover, the use of thermally imidized polyimide requires the release agent to withstand temperatures up to 300°C, at which point most release agents decompose. This significantly limits the selection and application range of release agents. Alternatively, a peeling method can be used: polyimide is spin-coated onto a substrate, and a metal frame is prepared on top using a seed layer electroplating method. Finally, the polyimide film is peeled off from the substrate. This method avoids the use of chemical reagents to damage the polyimide and can maintain the surface roughness of the film to a certain extent. However, peeling the polyimide film from the substrate applies external force to the polyimide film, thus affecting the film's performance. In addition, this peeling process cannot be performed by machine, which is a huge obstacle to mass production. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a polyimide thin film passive filter device and its preparation method, which solves the problem that the preparation methods of polyimide forming self-supporting films in the prior art will affect the performance of polyimide, resulting in a decrease in the performance of polyimide.

[0005] To achieve the above and other related objectives, the present invention provides a method for preparing a polyimide thin film passive optical filter device, the method comprising:

[0006] A semiconductor substrate is provided, and a dielectric layer and a polyimide thin film layer are sequentially formed on the front side of the semiconductor substrate;

[0007] A barrier layer is formed on the polyimide film layer, and the barrier layer and the polyimide film layer work together to filter light other than X-rays;

[0008] A first patterned photoresist layer is formed on the barrier layer to obtain a photolithographic pattern of the outer contour of the thin film.

[0009] Based on the first patterned photoresist layer, the barrier layer, the polyimide film layer and the dielectric layer are sequentially etched;

[0010] A second patterned photoresist layer is formed on the back side of the semiconductor substrate to obtain a photolithographic pattern of the inner contour of the thin film;

[0011] Based on the second patterned photoresist layer, the semiconductor substrate is etched using a deep reactive ion etching process to form an etching window;

[0012] Based on the etching window, the dielectric layer is removed using a dry etching process to obtain a polyimide thin film passive filter device.

[0013] Optionally, the semiconductor substrate is made of silicon, and the dielectric layer is made of silicon oxide or silicon nitride.

[0014] Optionally, the dielectric layer may be formed using a thermal oxidation process or a chemical vapor deposition process.

[0015] Optionally, the thickness of the dielectric layer is between between.

[0016] Optionally, the polyimide film layer is formed using a spin coating process.

[0017] Furthermore, the step of forming the polyimide film layer using a spin coating process includes:

[0018] Spin coating process: A polyimide material layer is spin-coated onto the medium layer at a spin speed between 1000 rpm and 8000 rpm.

[0019] Pre-baking process: Baking temperature is between 130℃ and 200℃;

[0020] Repeat the spin coating and pre-baking processes described above 0 to 5 times;

[0021] Hardening process: Harden in nitrogen or air for 20 to 60 minutes at a temperature between 280°C and 350°C.

[0022] Furthermore, during the pre-baking process, the obtained structure is placed on a hot plate and baked for 90s to 180s, or the obtained structure is placed in an oven and baked for 30min to 40min; the starting temperature of the hardening process is room temperature or the baking temperature of the pre-baking process, and the heating rate from the starting temperature to the hardening temperature is between 2℃ / min and 4℃ / min.

[0023] Optionally, the barrier layer may be formed using a sputtering process, an evaporation process, or a spin coating process.

[0024] Optionally, the barrier layer is etched using a dry ion beam etching process or a wet etching process; the polyimide film layer and the dielectric layer are etched using a dry etching process.

[0025] The present invention also provides a polyimide film passive optical filter device, which is prepared by the preparation method of polyimide film passive optical filter device described in any one of the above claims.

[0026] As described above, the polyimide film passive filter device and its fabrication method of the present invention can achieve precise control of the polyimide film thickness, perform arbitrary patterning, and obtain polyimide films of the required size and shape, while ensuring the roughness of the obtained polyimide film. In addition, the fabrication method is non-destructive to the polyimide film, and the polyimide film does not need to be peeled from the substrate, which greatly improves the yield of polyimide film. Finally, all processes of the fabrication method are MEMS processes, which is conducive to the mass production of products. Attached Figure Description

[0027] Figure 1 The diagram shows a process flow diagram of the preparation method of the polyimide film passive filter device of the present invention.

[0028] Figures 2 to 13 The diagram shows a cross-sectional view of each step in the preparation method of the polyimide film passive filter device of the present invention.

[0029] Component designation explanation

[0030] 100 Semiconductor substrate

[0031] 101 Dielectric Layer

[0032] 102 Polyimide film layer

[0033] 103 Barrier Layer

[0034] 104 First photoresist layer

[0035] 105 First patterned photoresist layer

[0036] 106 First Etching Window

[0037] 107 Second photoresist layer

[0038] 108 Second patterned photoresist layer

[0039] 109 Second Etching Window

[0040] 110 Etched Window

[0041] 111 Photolithographic pattern of the thin film outer contour

[0042] 112 Photolithographic pattern of the inner contour of the thin film

[0043] 113 Polyimide film passive optical filter device

[0044] Steps S1 to S7 Detailed Implementation

[0045] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] The terms “approximately,” “about,” or “nearly” as used herein should generally mean that a given value or error range is within 20%, preferably within 10%. Furthermore, the quantities provided herein may be approximate, and therefore mean that unless otherwise stated, they may be expressed using the terms “approximately,” “about,” or “nearly.” When a quantity, concentration, or other numerical value or parameter has a specified range, preferred range, or lists upper and lower ideal values, it should be considered as specifically disclosing all ranges consisting of any pairs of upper and lower limits or ideal values, regardless of whether such ranges are separately disclosed. For example, if a range of length X cm to Y cm is disclosed, it should be considered as disclosing a length of H cm, where H can be any real number between X and Y.

[0047] It is understood that terms such as “comprising,” “having,” and “containing,” as used herein, are open-ended terms, meaning including but not limited to. Furthermore, no embodiment or claim of this disclosure is required to achieve all the purposes, advantages, or features disclosed herein. In addition, the abstract and headings are merely for assisting in patent document searches and are not intended to limit the claims of this application.

[0048] Please see Figures 1 to 13 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be changed according to actual needs, and the layout of the components may also be more complex.

[0049] like Figure 1 As shown, this embodiment provides a method for fabricating a polyimide thin film passive optical filter device, the method comprising:

[0050] like Figures 1 to 3 As shown, step S1 is performed first, a semiconductor substrate 100 is provided, and a dielectric layer 101 (e.g., ...) is sequentially formed on the front side of the semiconductor substrate 100. Figure 2 (as shown) and polyimide film layer 102 (as shown) Figure 3 (As shown).

[0051] The semiconductor substrate 100 can be any existing semiconductor material suitable for fabricating passive optical filtering devices, such as silicon, germanium, germanium-silicon, silicon carbide, etc. In this embodiment, silicon is the preferred material for the semiconductor substrate 100. The semiconductor substrate 100 subsequently serves as the supporting body for the passive optical filtering device, and its thickness can be selected according to actual needs to achieve the desired support effect.

[0052] The dielectric layer 101 serves as an etch stop layer and is generally selected from materials with a high etch selectivity ratio compared to the semiconductor substrate, such as silicon oxide or silicon nitride. Furthermore, in subsequent fabrication processes, dry etching of the dielectric layer 101 is required when releasing the passive filter thin film structure; therefore, the material of the dielectric layer 101 must also be selected from materials with a high etch selectivity ratio compared to the polyimide thin film layer. In this embodiment, when the semiconductor substrate 100 is made of silicon, the dielectric layer 101 is preferably made of silicon oxide, as silicon oxide has a good etch selectivity ratio with silicon and also with the polyimide material. The thickness of the dielectric layer 101 is generally selected to be between... between.

[0053] The dielectric layer 101 can be formed using existing conventional processes, such as thermal oxidation, LPCVD, and PECVD chemical deposition processes. In this embodiment, thermal oxidation is preferably used to form the dielectric layer, as it produces a dielectric layer of high quality and good uniformity, laying a good foundation for the subsequent release of the polyimide film layer.

[0054] The polyimide film layer 102 can be formed using existing conventional processes, such as spin coating. In this embodiment, the spin coating process for forming the polyimide film layer 102 includes: spin coating: a polyimide material layer is spin-coated onto the dielectric layer 101 at a rotation speed between 1000 rpm and 8000 rpm; pre-baking: the baking temperature is between 130°C and 200°C. In this step, hot plate baking or oven baking can be used. When using hot plate baking, the baking time is between 90 seconds and 180 seconds; when using oven baking, the baking time is between 30 minutes and 40 minutes; repeating the process. Repeat the spin coating and pre-baking processes several times. The number of repetitions depends on the specific process and the thickness of the polyimide film layer. Repetitions may be omitted or repeated multiple times, generally between 0 and 5 times. Curing process: Cure in a nitrogen or air environment for 20 to 60 minutes at a curing temperature between 280°C and 350°C. In this step, the starting temperature of the curing process can be room temperature or the baking temperature of the pre-baking process. The heating rate from the starting temperature to the curing temperature is between 2°C / min and 4°C / min.

[0055] like Figure 1 and Figure 4 As shown, step S2 is then performed to form a blocking layer 103 on the polyimide film layer 102. The blocking layer 103 and the polyimide film layer 102 work together to filter light other than X-rays.

[0056] As an example, the barrier layer 103 can be formed using processes such as sputtering, evaporation, or spin coating. The thickness of the barrier layer 103 needs to be specifically selected and is not excessively limited here.

[0057] like Figure 1 and Figure 6 As shown, step S3 is then performed to form a first patterned photoresist layer 105 on the barrier layer 103, thereby obtaining a photolithographic pattern 111 of the outer contour of the thin film.

[0058] like Figure 5 and Figure 6 As shown, as an example, the specific steps for forming the first patterned photoresist layer 105 include: Figure 5As shown, photoresist is uniformly coated onto the surface of the barrier layer 103. Then, the resulting structure covered with photoresist is transferred from the coating machine to an oven for coating and baking to evaporate the moisture in the photoresist, fix the photoresist, and form the first photoresist layer 104; as shown Figure 6 As shown, the first photoresist layer 104 is then subjected to photolithography, development and post-baking to form a first patterned photoresist layer 105, resulting in a photolithographic pattern 111 of the outer contour of the thin film. The first etch window 106 formed by the first patterned photoresist layer 105 exposes the barrier layer 103, and the photolithographic pattern 111 of the outer contour of the thin film covers the barrier layer 103.

[0059] like Figure 1 and Figure 9 As shown, step S4 is then performed, in which the barrier layer 103, the polyimide film layer 102, and the dielectric layer 101 are sequentially etched based on the first patterned photoresist layer 105. Specifically, the barrier layer 103, the polyimide film layer 102, and the dielectric layer 101 are sequentially etched based on the first etching window 106.

[0060] like Figure 7 As shown, the barrier layer 103 can be etched using either dry plasma beam etching (IBE) or wet etching.

[0061] like Figure 8 As shown, the polyimide thin film layer 102 can be etched using a dry etching process, wherein the dry etching gas can be an oxygen-based gas.

[0062] like Figure 9 As shown, the dielectric layer 101 can be etched using a dry etching process.

[0063] It should be noted that after etching the barrier layer 103, the polyimide film layer 102 and the dielectric layer 101 in sequence, the process also includes the step of removing the first patterned photoresist layer 105.

[0064] like Figure 1 and Figure 11 As shown, step S5 is then performed to form a second patterned photoresist layer 108 on the back side of the semiconductor substrate 100, thereby obtaining a photolithographic pattern 112 of the inner contour of the thin film.

[0065] like Figure 10 and Figure 11 As shown, as an example, the specific steps for forming the second patterned photoresist layer 108 include: Figure 10As shown, photoresist is uniformly coated on the back side of the semiconductor substrate 100. Then, the resulting structure covered with photoresist is transferred from the coating machine to an oven for post-coating baking to evaporate the moisture in the photoresist, fix the photoresist, and form a second photoresist layer 107; as shown. Figure 11 As shown, the second photoresist layer 107 is then subjected to photolithography, development and post-baking to form a second patterned photoresist layer 108, resulting in a photolithographic pattern 112 of the inner contour of the thin film. The second etch window 109 formed by the second patterned photoresist layer 108 exposes the semiconductor substrate 100, and the photolithographic pattern 112 of the inner contour of the thin film exposes the semiconductor substrate 100.

[0066] like Figure 1 and Figure 12 As shown, step S6 is then performed, whereby the semiconductor substrate 100 is etched using a deep reactive ion etching (DRIE) process based on the second patterned photoresist layer 108 to form an etching window 110. Since DRIE has a good etching selectivity for the dielectric layer 101, the etching of the semiconductor substrate 100 stops on the surface of the dielectric layer 101 after completion, maintaining the surface integrity of the dielectric layer 101 and not affecting its quality.

[0067] In this embodiment, when the semiconductor substrate 100 is made of silicon and the dielectric layer 101 is made of silicon oxide, SF6 and C4F8 etching gases can be used for DRIE etching, which achieves the best etching effect.

[0068] like Figure 1 and Figure 13 As shown, in step S7, based on the etching window 110, a dry etching process is used to remove the dielectric layer 101, thereby releasing the polyimide film layer 102 and obtaining the polyimide film passive filter device 113. Because the dielectric layer obtained in the above DRIE etching step has good surface integrity and minimal damage, combined with the excellent etching selectivity of the dry etching in this step, the polyimide film layer 102 can be perfectly released without affecting the surface roughness and uniformity of the polyimide film layer, nor introducing defects into the polyimide film layer.

[0069] Thus, the preparation method of this embodiment yields a polyimide thin film passive filter device. This method allows for precise control of the polyimide film thickness, enables arbitrary patterning to obtain polyimide films of the desired size and shape, and ensures the roughness of the resulting polyimide film. Furthermore, this preparation method is non-destructive to the polyimide film, eliminating the need to peel the film from the substrate, significantly improving the yield of the polyimide film. Finally, all processes in this preparation method are MEMS processes, which is beneficial for mass production.

[0070] This embodiment also provides a polyimide film passive optical filter device, which is prepared using the preparation method of the polyimide film passive optical filter device of this embodiment.

[0071] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0072] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a polyimide thin film passive optical filter device, characterized in that, The preparation method includes: A semiconductor substrate is provided, and a dielectric layer and a polyimide thin film layer are sequentially formed on the front side of the semiconductor substrate; A barrier layer is formed on the polyimide film layer, and the barrier layer and the polyimide film layer work together to filter light other than X-rays; A first patterned photoresist layer is formed on the barrier layer to obtain a photolithographic pattern of the outer contour of the thin film. Based on the first patterned photoresist layer, the barrier layer, the polyimide film layer and the dielectric layer are sequentially etched; A second patterned photoresist layer is formed on the back side of the semiconductor substrate to obtain a photolithographic pattern of the inner contour of the thin film; Based on the second patterned photoresist layer, the semiconductor substrate is etched using a deep reactive ion etching process to form an etching window; Based on the etching window, the dielectric layer is removed using a dry etching process to obtain a polyimide thin film passive filter device.

2. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The semiconductor substrate is made of silicon, and the dielectric layer is made of silicon oxide or silicon nitride.

3. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The dielectric layer is formed using a thermal oxidation process or a chemical vapor deposition process.

4. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The thickness of the dielectric layer is between between.

5. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The polyimide film layer is formed using a spin coating process.

6. The method for preparing the polyimide thin film passive filter device according to claim 5, characterized in that, The steps for forming the polyimide film layer using a spin coating process include: Spin coating process: A polyimide material layer is spin-coated onto the medium layer at a spin speed between 1000 rpm and 8000 rpm. Pre-baking process: Baking temperature is between 130℃ and 200℃; Repeat the spin coating and pre-baking processes described above 0 to 5 times; Hardening process: Harden in nitrogen or air for 20 to 60 minutes at a temperature between 280°C and 350°C.

7. The method for preparing the polyimide thin film passive filter device according to claim 6, characterized in that: During the pre-baking process, the obtained structure is placed on a hot plate and baked for 90s to 180s, or placed in an oven and baked for 30min to 40min; the starting temperature of the hardening process is room temperature or the baking temperature of the pre-baking process, and the heating rate from the starting temperature to the hardening temperature is between 2℃ / min and 4℃ / min.

8. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The barrier layer is formed using sputtering, evaporation, or spin coating processes.

9. The method for preparing the polyimide thin film passive filter device according to claim 1, characterized in that: The barrier layer is etched using a dry ion beam etching process or a wet etching process; the polyimide film layer and the dielectric layer are etched using a dry etching process.

10. A passive optical filter device with polyimide film, characterized in that, The polyimide film passive filter device is prepared by the preparation method of the polyimide film passive filter device according to any one of claims 1 to 9.

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