A vanadium oxide etching method applied to a non-cooled infrared detector

Abstract

The application discloses a vanadium oxide etching method of a non-refrigeration infrared detector, and the method comprises the following steps: 1) providing a substrate, and forming a vanadium oxide film and a silicon nitride film on the surface of the substrate; 2) forming a patterned photoresist on the vanadium oxide film and the silicon nitride film; 3) etching the silicon nitride film to a depth of 1 / 3-2 / 3; 4) removing the photoresist; and 5) etching the vanadium oxide film to form a required vanadium oxide film structure by taking the silicon nitride film as a hard mask. The method removes the photoresist before etching the VOx film, and the silicon nitride is taken as the hard mask for etching, so that the influence of the traditional process of removing the photoresist after etching the VOx film on the vanadium oxide is avoided, meanwhile, the silicon nitride is taken as the hard mask and the protective layer of the VOx film and remains on the film, and it is not necessary to remove the silicon nitride. The quality of the vanadium oxide photosensitive layer is improved, the removing mode is diversified, and the device performance is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to a vanadium oxide etching method for use in uncooled infrared detectors. Background Technology

[0002] An uncooled detector is a detector that operates at room temperature and converts incident infrared thermal radiation signals into electrical signals. It requires no cooling device, operates at room temperature, and offers numerous advantages such as fast start-up, low power consumption, small size, light weight, long lifespan, and low cost. Among these, the vanadium oxide microbolometer is the most widely used uncooled detector, finding broad application in both military and civilian sectors.

[0003] Vanadium oxide thin film deposition technology is relatively mature, and a wealth of information has been accumulated in its research as an optical switch, thermochromic, electrochromic, and phase transition recording material. Honeywell chose vanadium oxide thin films when developing its radiometric calorimeter array. Its key characteristics include: deposition conditions compatible with silicon integrated circuits; excellent deposition on support materials such as silicon nitride films, which also serve as passivation materials; moderate resistivity, allowing for films with thicknesses ranging from 50 nm to 100 nm and resistances of tens of kiloohms; moderate 1 / f noise when electrical contacts are properly fabricated; a TCR many times greater than that of metal thin films, typically -2% / K, with a maximum of approximately -6% / K; and excellent optical properties, which are beneficial for achieving high radiation absorptivity.

[0004] Etching is one of the key processes in the fabrication of semiconductor optoelectronic devices, and photoresist is typically used as a mask during etching. However, photoresist used as a mask is prone to carbonization and degradation during etching, making it difficult to completely remove from the device surface with resist remover or acetone. This affects subsequent device processes and leads to performance degradation. Furthermore, even when the photoresist can be completely removed, the morphology of the etched pattern can significantly impact subsequent device processes. To reduce the complexity of device fabrication and improve fabrication efficiency, it is crucial to study the impact of better etching techniques on the photoresist mask and the sidewall morphology of the etched pattern.

[0005] There are generally two methods for forming mesa and preparing contact holes: dry etching and wet etching. Wet etching is a simple and non-destructive process, but it inevitably involves drilling and is isotropic etching. Dry etching is anisotropic and has almost no drilling, but it inevitably involves etching damage. Summary of the Invention

[0006] The purpose of this invention is to provide a process improvement scheme in the manufacturing process of vanadium oxide uncooled infrared detectors. By using silicon nitride as a hard mask for etching through pre-removal of resist, the influence of the post-removal process on vanadium oxide is avoided, the resist removal method is diversified, and thus the device performance is effectively improved.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A vanadium oxide etching method for use in uncooled infrared detectors includes:

[0009] 1) Provide a substrate, on which a vanadium oxide thin film and a silicon nitride thin film are formed;

[0010] 2) Spin-coating photoresist onto the vanadium oxide film and the silicon nitride film;

[0011] 3) A patterned photoresist mask is formed using a photomask;

[0012] 4) Etch 1 / 3 to 2 / 3 of the silicon nitride film to transfer the pattern of the photoresist onto the silicon nitride film;

[0013] 5) Remove the photoresist;

[0014] 6) A silicon nitride thin film is used as a hard mask to etch a vanadium oxide thin film to form the desired structure.

[0015] Furthermore, the vanadium oxide film has a thickness between 50 and 200 nm, and the silicon nitride film has a thickness between 100 and 500 nm; the vanadium oxide film is prepared by ion beam sputtering, and the silicon nitride film is prepared by chemical vapor deposition.

[0016] Furthermore, the thickness of the photoresist is between 0.5 μm and 5 μm.

[0017] Furthermore, the photomask is determined according to the vanadium oxide design requirements, and the patterned photoresist covers the vanadium oxide areas required by the design, while the remaining areas are exposed to the outside.

[0018] Furthermore, the pattern of the photoresist is transferred onto the silicon nitride film, that is, the silicon nitride not protected by the photoresist is etched to a depth of 1 / 3 to 2 / 3 of the thickness of the silicon nitride, while the silicon nitride protected by the photoresist is not etched and remains unchanged.

[0019] Furthermore, the silicon nitride thin film is etched using inductively coupled plasma etching.

[0020] Furthermore, the method for removing photoresist employs a dry removal process to completely remove the photoresist.

[0021] Furthermore, the silicon nitride film serves as a hard mask, meaning that photoresist is not used as a mask and etching is performed directly. Due to the protection of the silicon nitride film, the vanadium oxide areas required by the design are preserved, while the vanadium oxide areas not required by the design are etched away.

[0022] Furthermore, the vanadium oxide thin film is etched using inductively coupled plasma etching.

[0023] The present invention has the following beneficial effects:

[0024] (1) Unlike existing etching methods, this invention adopts techniques such as pre-removal of photoresist and using silicon nitride as a hard mask instead of photoresist as a mask to etch vanadium oxide during the etching process, which effectively avoids the impact of the post-removal process on vanadium oxide.

[0025] (2) In the process of etching vanadium oxide, the present invention realizes the etching method of replacing the photoresist mask with a silicon nitride hard mask to protect vanadium oxide through common patterning methods. It can eliminate the negative impact of the photoresist removal process on vanadium oxide, making the photoresist removal method more diverse and flexibly selectable according to the actual situation. Attached Figure Description

[0026] Figure 1 Cross-sectional view of vanadium oxide uncooled infrared detector structure and schematic diagram of vanadium oxide etching process;

[0027] Figure 2 This is a schematic diagram of the coating process in the vanadium oxide etching method of the present invention;

[0028] Figure 3 This is a schematic diagram of the patterned photoresist process in the vanadium oxide etching method of the present invention;

[0029] Figure 4 This is a schematic diagram of the etching process of the silicon nitride thin film by etching 1 / 3 to 2 / 3 of the silicon nitride film in the vanadium oxide etching method of the present invention;

[0030] Figure 5 This is a schematic diagram of the photoresist removal process in the vanadium oxide etching method of the present invention;

[0031] Figure 6 This is a schematic diagram of the etching process of vanadium oxide thin film using silicon nitride thin film as hard mask in the vanadium oxide etching method of the present invention.

[0032] Figure 7 This is a schematic diagram of the final etching effect in the vanadium oxide etching method of the present invention.

[0033] Wherein: 100, vanadium oxide uncooled infrared detector; 200, vanadium oxide etched structure; 1, silicon nitride substrate; 2, vanadium oxide photosensitive layer; 3, silicon nitride protective layer; 4, photoresist layer; 5, photomask; 21, patterned vanadium oxide photosensitive layer; 31, patterned silicon nitride protective layer A; 32, patterned silicon nitride protective layer B; 33, patterned silicon nitride protective layer C; 41, patterned photoresist layer A; 42, patterned photoresist layer B. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] See Figures 1 to 7 A vanadium oxide etching method for uncooled infrared detectors according to this disclosure includes:

[0036] Step 1, see Figure 1 The silicon nitride substrate 1 is provided, and the vanadium oxide photosensitive layer 2 and the silicon nitride protective layer 3 are grown on the surface of the silicon nitride substrate 1.

[0037] Step 2, see Figure 2 A photoresist layer 4 is spin-coated onto the silicon nitride protective layer 3;

[0038] Step 3, see Figure 3 A patterned photoresist layer A41 is formed through the photomask 5;

[0039] Step four, see Figure 4 Etch 1 / 3 to 3 / 2 of the silicon nitride protective layer 3 to transfer the pattern of the photoresist to the patterned silicon nitride protective layer A 31;

[0040] Step 5, see Figure 5 While etching 1 / 3 to 3 / 2 of the silicon nitride protective layer 3, the patterned photolithography layer A41 is also etched to form a patterned photoresist layer B42, and the patterned photoresist layer B42 is removed.

[0041] Step Six, see Figure 5 and Figure 6 The patterned silicon nitride protective layer A 31 is etched until a patterned silicon nitride protective layer B 32 is formed. Using the patterned silicon nitride protective layer B 32 as a mask, the vanadium oxide photosensitive layer 2 is hard etched to form the patterned silicon nitride protective layer B 32. Figure 7 The final etched morphology.

[0042] The silicon nitride substrate 1 is provided with the vanadium oxide photosensitive layer 2, the thickness of the vanadium oxide photosensitive layer 2 is between 50 and 200 nm, and the vanadium oxide photosensitive layer 2 is prepared by ion beam sputtering.

[0043] The silicon nitride protective layer 3 is provided on the vanadium oxide photosensitive layer 2. The thickness of the silicon nitride protective layer 3 is between 100 and 500 nm. The silicon nitride protective layer 3 is prepared by chemical vapor deposition.

[0044] The photoresist layer 4 is spin-coated onto the silicon nitride protective layer 3, and the thickness of the photoresist layer 4 is between 0.5 μm and 5 μm.

[0045] The patterned photoresist layer A 41 is formed through the photomask 5 using a photolithography process, involving exposure, development, and post-baking steps. The photomask 5 is determined according to the vanadium oxide design requirements; see [reference needed]. Figure 3 The patterned photoresist layer A 41 and the patterned photoresist layer B 42 cover the vanadium oxide area required by the design, while the remaining areas are exposed to the outside.

[0046] The pattern of the photoresist is transferred onto the silicon nitride protective layer 3, that is, the silicon nitride protective layer not protected by the photoresist is etched, and the silicon nitride protective layer 3 is etched to a depth of 1 / 3 to 2 / 3. The silicon nitride protective layer 3 protected by the photoresist is not etched and remains unchanged, forming the patterned silicon nitride protective layer A 31.

[0047] The patterned photoresist layer B 42 is formed by etching 1 / 3 to 3 / 2 of the thickness of the silicon nitride protective layer 3 while the patterned photoresist layer A 41 is also etched.

[0048] The etching method is inductively coupled plasma etching.

[0049] The method for removing photoresist employs a dry removal process to completely remove the photoresist.

[0050] The silicon nitride protective layer A 31 serves as a mask, meaning that photoresist is not used as a mask for protection; etching is performed directly. Due to the difference in thickness, a portion of the unnecessary silicon nitride protective layer A 31 is etched away, while the portion that needs to be retained is preserved to form a patterned silicon nitride protective layer B 32. The patterned silicon nitride protective layer B 32 serves as a mask to protect the vanadium oxide photosensitive layer 2 required by the design. After etching, the vanadium oxide portion required by the design is preserved, forming a patterned vanadium oxide photosensitive layer 21, while the vanadium oxide portion not required by the design is etched away. Simultaneously, the patterned silicon nitride protective layer B 32 is also etched to form a patterned silicon nitride protective layer C 33, thereby ultimately forming the desired structure.

[0051] The etching method is inductively coupled plasma etching.

[0052] Example 1

[0053] A microbridge structure array was fabricated on an 8-inch wafer using a vanadium oxide uncooled detector MEMS process. A 100nm vanadium oxide thin film and a 300nm silicon nitride thin film were deposited on the wafer. Next, 1µm photoresist was spin-coated onto the wafer, and a patterned photoresist mask was formed through exposure and development processes. The silicon nitride film not protected by the photoresist mask was etched to a depth of 200nm. All photoresist on the wafer was removed using a dry stripping method, resulting in silicon nitride films of varying thicknesses (the required thickness of the silicon nitride film on the vanadium oxide layer is 300nm, and the thickness of the silicon nitride film on the vanadium oxide layer to be removed is...). The film thickness is 100 nm. Then, without photoresist protection, silicon nitride film etching is performed directly to a depth of 100 nm. At this point, there is no silicon nitride film on the required vanadium oxide, while the silicon nitride film on the vanadium oxide to be removed has a thickness of 200 nm. Then, the silicon nitride film is used directly as a hard mask to etch the vanadium oxide film. The etching ratio of silicon nitride to vanadium oxide is adjusted to 1:1. At this point, the required vanadium oxide area is preserved due to the protection of the silicon nitride film (there is still a 100 nm silicon nitride film on it), while the vanadium oxide area that is not required by the design is etched away to form the required structure.

[0054] Comparative Example 1

[0055] Similar to Example 1, a microbridge structure array was fabricated on an 8-inch wafer using a vanadium oxide uncooled detector MEMS process. A 100nm vanadium oxide thin film and a 100nm silicon nitride thin film were deposited on the wafer. Next, a 2µm photoresist was spin-coated onto the wafer, and a patterned photoresist mask was formed through exposure, development, and other processes. Then, the silicon nitride thin film was etched to a depth of 100nm. At this point, the required vanadium oxide no longer had a silicon nitride film, while the silicon nitride film on the vanadium oxide to be removed had a thickness of 100nm. Then, the vanadium oxide thin film was etched to a depth of 100nm. At this point, the required vanadium oxide area was preserved due to the protection of the photoresist mask (at this point, there was still a 100nm silicon nitride film on it), while the vanadium oxide area that was not designed was etched away. Finally, all the photoresist on the wafer was removed by a dry photoresist removal method to form the desired structure.

[0056] Comparing Example 1 and Comparative Example 1, the vanadium oxide surface in Example 1 was smoother and there were no chemical residues, while Comparative Example 1 had some minor chemical residues due to the degumming process.

[0057] In Example 1, the method for removing photoresist can be either wet or dry. The choice of method will not affect the vanadium oxide surface. In Comparative Example 1, if wet removal is used, it will cause corrosion and more chemical residue on the vanadium oxide surface.

[0058] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A vanadium oxide etching method for use in uncooled infrared detectors, characterized in that, The etching method includes: Step 1: Provide a substrate, and form a vanadium oxide thin film and a silicon nitride thin film on the surface of the substrate; Step 2: Spin-coat photoresist onto the vanadium oxide thin film and silicon nitride thin film; Step 3: Form a patterned photoresist using a photomask; Step 4: The silicon nitride thin film is etched using inductively coupled plasma etching to a depth of 1 / 3 to 2 / 3 of the thickness of the silicon nitride, thereby transferring the pattern of the photoresist onto the silicon nitride thin film. Step 5: Remove the photoresist; Step 6: Using a silicon nitride thin film as a hard mask, the vanadium oxide thin film is etched using inductively coupled plasma to form the desired structure.

2. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 1: The vanadium oxide thin film was prepared by ion beam sputtering and its thickness was between 50 and 200 nm. The silicon nitride thin film is prepared by chemical vapor deposition and has a thickness between 100 and 500 nm.

3. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 2: The thickness of the photoresist is between 0.5µm and 5µm.

4. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 3: The photolithography mask is determined according to the vanadium oxide design requirements; The patterned photoresist is used to cover the vanadium oxide areas required by the design, while the remaining areas are exposed to the outside.

5. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 4: The silicon nitride protected by the photoresist was not etched and remained intact.

6. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 4: The pattern of the photoresist is transferred onto the silicon nitride film by etching the silicon nitride that is not protected by the photoresist.

7. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that, In step 5: The photoresist was completely removed using a dry stripping method.

8. A vanadium oxide etching method for uncooled infrared detectors according to any one of claims 1-7, characterized in that, In step 6: Etching is performed directly without using photoresist as a mask. The silicon nitride film protects the vanadium oxide areas required by the design, while the vanadium oxide areas not required by the design are etched away.

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