Vanadium oxide etching method applied to uncooled infrared detector

Abstract

The invention discloses a vanadium oxide etching method for an uncooled infrared detector, and the method comprises the steps: 1) providing a substrate, and forming a vanadium oxide film and a silicon nitride film on the surface of the substrate; 2) forming patterned photoresist on the vanadium oxide thin film and the silicon nitride thin film; 3) etching the silicon nitride thin film, wherein the depth is 1 / 3-2 / 3; 4) removing the photoresist; and 5) etching the vanadium oxide thin film by using the silicon nitride thin film as a hard mask to form the required vanadium oxide thin film structure. According to the method, the photoresist is removed before the VOx thin film is etched, and the silicon nitride is used as the hard mask for etching, so that the influence on the vanadium oxide in the traditional process of removing the photoresist after the VOx thin film is etched is avoided, and meanwhile, the silicon nitride is left on the thin film as the hard mask and a protective layer of the VOx thin film and does not need to be removed. The quality of the vanadium oxide photosensitive layer is improved, meanwhile, the photoresist removing modes are diversified, and the performance of the device is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor manufacturing, and in particular to a vanadium oxide etching method applied to an uncooled infrared detector. Background Art

[0002] An uncooled detector is a detector that works at room temperature and can convert incident infrared thermal radiation signals from the outside into electrical signals. It does not require a refrigeration device and can work at room temperature. It has many advantages, such as fast startup, low power consumption, small size, light weight, long life, and low cost. Among them, the vanadium oxide microbolometer is the uncooled detector with the highest market share and has been widely used in both military and civilian fields.

[0003] Since the deposition technology of vanadium oxide thin films is relatively mature, a wealth of information has been accumulated in the research process of using them as optical switches, thermochromic materials, electrochromic materials, and phase change recording materials. Honeywell selected vanadium oxide thin films when developing the bolometer array. Its basic characteristics include: the deposition conditions are compatible with the silicon integration process; it can be well deposited on supporting materials such as silicon nitride films, and silicon nitride is also its passivation material; the resistivity is moderate, and thin films with a thickness of 50nm to 100nm and a resistance of tens of kiloohms can be obtained; when the electrical contact is prepared reasonably, the 1 / f noise is moderate; the TCR is many times larger than that of metal films, with a typical value of -2% / K and a maximum value of about -6% / K; it has good optical properties and is conducive to obtaining high radiation absorption rates.

[0004] Etching is one of the key processes in the manufacturing process of semiconductor optoelectronic devices. In the etching process, photoresist is usually used as a mask. However, the photoresist used as a mask is prone to carbonization and denaturation during the etching process, so that it is difficult to completely remove it with a degumming solution or acetone when it adheres to the device surface, thereby affecting the subsequent process of the device and causing the device performance to deteriorate. In addition, when the photoresist can be removed cleanly, the morphology of the etched pattern will also have a great impact on the subsequent process of the device. In order to reduce the complexity of device manufacturing and improve the efficiency of device preparation, it is crucial to study the impact of better etching technology on the morphology of the photoresist mask and the sidewall morphology of the etched pattern.

[0005] There are usually two methods for mesa forming and contact hole preparation: dry etching and wet etching. The wet etching process is simple and damage-free, but it inevitably has undercutting and isotropic. The dry etching process is anisotropic, with almost no undercutting, but it inevitably has etching damage. Summary of the invention

[0006] The purpose of the present invention is to provide a process improvement scheme in the manufacturing process of vanadium oxide uncooled infrared detectors. By using the front stripping method, silicon nitride is etched as a hard mask, thereby avoiding the influence of the post-stripping process on vanadium oxide, making the stripping method more diverse, thereby effectively improving the device performance.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A vanadium oxide etching method for an uncooled infrared detector, comprising:

[0009] 1) providing a substrate, and forming a vanadium oxide film and a silicon nitride film on the surface of the substrate;

[0010] 2) spin coating photoresist on the vanadium oxide film and the silicon nitride film;

[0011] 3) forming a patterned photoresist mask through a photolithography mask;

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

[0013] 5) removing the photoresist;

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

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

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

[0017] Furthermore, the photolithography mask is determined according to the design requirements of the vanadium oxide, and the patterned photoresist covers the vanadium oxide parts required by the design, and the remaining parts are exposed to the outside.

[0018] Furthermore, the pattern of the photoresist is transferred to 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 as it is.

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

[0020] Furthermore, the method for removing the photoresist adopts dry stripping to completely remove the photoresist.

[0021] Furthermore, the silicon nitride film is used as a hard mask, that is, etching is performed directly without using a photoresist as a mask. Due to the protection of the silicon nitride film, the vanadium oxide parts required by the design are retained, while the vanadium oxide parts not required by the design are etched away.

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

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

[0024] (1) Different from the existing etching method, the present invention adopts the technical means of etching vanadium oxide by pre-stripping and using silicon nitride as a hard mask instead of photoresist as a mask to etch vanadium oxide, thereby effectively avoiding the influence of post-stripping 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 the vanadium oxide through common graphical means, and there is no need to consider the negative impact of the stripping process on the vanadium oxide, so that the stripping method becomes diverse and can be flexibly selected according to actual conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The structural cross section of the vanadium oxide uncooled infrared detector and the schematic diagram of the vanadium oxide etching process;

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

[0028] Figure 3 It 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 process of etching 1 / 3 to 2 / 3 of the silicon nitride film in the vanadium oxide etching method of the present invention;

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

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

[0032] Figure 7 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 etching structure; 1, silicon nitride substrate; 2, vanadium oxide photosensitive layer; 3, silicon nitride protective layer; 4, photoresist layer; 5, photolithography mask; 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 DESCRIPTION

[0034] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] See also Figures 1 to 7 According to the present disclosure, a vanadium oxide etching method for an uncooled infrared detector includes:

[0036] Step 1, see Figure 1 , providing the silicon nitride substrate 1, and growing the vanadium oxide photosensitive layer 2 and the silicon nitride protective layer 3 on the surface of the silicon nitride substrate 1;

[0037] Step 2, see Figure 2 , spin coating a photoresist layer 4 on the silicon nitride protective layer 3;

[0038] Step 3, see Figure 3 , forming a patterned photoresist layer A 41 through the photolithography mask 5;

[0039] Step 4, see Figure 4 , etching 1 / 3 to 3 / 2 of the silicon nitride protective layer 3, transferring 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 protection layer 3, the patterned photoresist layer A41 is also etched to form a patterned photoresist layer B42, and the patterned photoresist layer B42 is removed;

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

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

[0043] The silicon nitride protective layer 3 is disposed 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 on the silicon nitride protection layer 3 , and the thickness of the photoresist layer 4 is between 0.5 um and 5 um.

[0045] The patterned photoresist layer A 41 is formed by the photolithography mask 5 through the photolithography process, exposure, development, post-baking and other steps. The photolithography mask 5 is determined according to the design requirements of vanadium oxide. Figure 3 The patterned photoresist layer A 41 and the patterned photoresist layer B 42 cover the vanadium oxide parts required by the design, and the rest of the parts are exposed to the outside.

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

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

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

[0049] The method for removing the photoresist adopts dry stripping to completely remove the photoresist.

[0050] The silicon nitride protective layer A 31 is used as a mask, that is, etching is performed directly without using a photoresist as a mask for protection. Due to different thicknesses, a portion of the silicon nitride protective layer A 31 that is not needed is etched away, and another portion of the silicon nitride protective layer A 31 that needs to be retained is retained to form a patterned silicon nitride protective layer B 32. The patterned silicon nitride protective layer B 32 is used as a mask to protect the vanadium oxide photosensitive layer 2 of the portion required by the design. After etching, the vanadium oxide portion required by the design is retained to form a patterned vanadium oxide photosensitive layer 21, while the vanadium oxide portion that is not needed by the design is etched away; at the same time, the patterned silicon nitride protective layer B 32 is also synchronously etched to form a patterned silicon nitride protective layer C 33, thereby finally forming the desired structure.

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

[0052] Example 1

[0053] A microbridge structure array is prepared on an 8-inch wafer by a vanadium oxide uncooled detector MEMS process, and a 100nm vanadium oxide film and a 300nm silicon nitride film are deposited on the wafer; then a 1um photoresist is spin-coated on the wafer, and a patterned photoresist mask is formed by processes such as exposure and development; the silicon nitride film not protected by the photoresist mask is etched to a depth of 200nm, and all the photoresist on the wafer is removed by a dry stripping method, so that the 300nm silicon nitride film forms silicon nitride films of different thicknesses (the required silicon nitride film thickness on the vanadium oxide is 300nm, and the silicon nitride film on the vanadium oxide to be removed is 200nm). The film thickness is 100nm); then, the silicon nitride film is directly etched without photoresist protection, and the etching depth is 100nm. At this time, there is no silicon nitride film on the required vanadium oxide, and the thickness of the silicon nitride film on the vanadium oxide to be removed is 200nm); at this time, the silicon nitride film is directly used as a hard mask to etch the vanadium oxide film, and the etching ratio of silicon nitride to vanadium oxide is adjusted to 1:1. At this time, the required vanadium oxide part is retained due to the protection of the silicon nitride film (at this time, there is still 100nm of silicon nitride film on it), and the unnecessary vanadium oxide part is etched away to form the required structure.

[0054] Comparative Example 1

[0055] The same as Example 1, a microbridge structure array is prepared on an 8-inch wafer by a vanadium oxide non-cooled detector MEMS process, and a 100nm vanadium oxide film and a 100nm silicon nitride film are deposited on the wafer; then a 2um photoresist is spin-coated on the wafer, and a patterned photoresist mask is formed by processes such as exposure and development; then the silicon nitride film is etched to a depth of 100nm, at which time there is no silicon nitride film on the required vanadium oxide, and the thickness of the silicon nitride film on the vanadium oxide to be removed is 100nm; then the vanadium oxide film is etched to a depth of 100nm, at which time the required vanadium oxide portion is retained due to the protection of the photoresist mask (at this time there is still a 100nm silicon nitride film on it), and the vanadium oxide portion that is not required by design is etched and removed, and finally all the photoresists on the wafer are removed by a dry stripping method to form the required structure.

[0056] By observing Example 1 and Comparative Example 1, it is found that the surface of vanadium oxide in Example 1 is relatively flat and has no chemical residues, while some slight chemical residues exist in Comparative Example 1 due to the degumming process.

[0057] In Example 1, the method for removing the photoresist can be either wet stripping or dry stripping, and the selection of the stripping method will not affect the surface of the vanadium oxide. If wet stripping is used in Comparative Example 1, it will cause corrosion of the vanadium oxide surface and more chemical residues.

[0058] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A vanadium oxide etching method for an uncooled infrared detector, characterized in that: The etching method comprises: Step 1, providing a substrate, and forming a vanadium oxide film and a silicon nitride film on the surface of the substrate; Step 2, spin coating photoresist on the vanadium oxide film and the silicon nitride film; Step 3, forming a patterned photoresist through a photolithography mask; Step 4, etching the silicon nitride film to a depth no greater than 2 / 3 of the thickness of the silicon nitride film, and transferring the pattern of the photoresist to the silicon nitride film; Step 5, removing the photoresist; Step 6: Use the silicon nitride film as a hard mask to etch the vanadium oxide film to form a desired structure.

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

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

4. The vanadium oxide etching method for an uncooled infrared detector according to claim 1, characterized in that: In step 3: The photolithography mask is determined according to the design requirements of vanadium oxide; The patterned photoresist is used to cover the vanadium oxide parts required by the design, and the remaining parts 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 etching depth is 1 / 3 to 2 / 3 of the thickness of the silicon nitride, and the silicon nitride protected by the photoresist is not etched and remains as it is.

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 to 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 is completely removed by dry stripping.

8. The vanadium oxide etching method for uncooled infrared detectors according to claim 1, characterized in that: In step 6: By directly etching without using a photoresist as a mask, the vanadium oxide parts required by the design are retained through the protection of the silicon nitride film, while the vanadium oxide parts not required by the design are etched away.

9. A vanadium oxide etching method for an uncooled infrared detector according to any one of claims 1 to 8, characterized in that: In step 4: The silicon nitride film is etched by inductively coupled plasma etching.

10. A vanadium oxide etching method for an uncooled infrared detector according to any one of claims 1 to 8, characterized in that: In step 6: The vanadium oxide film is etched by inductively coupled plasma etching.

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