Etching method for back cavity of micro hot plate structure

Abstract

The invention belongs to the field of semiconductor manufacturing, and provides an etching method for a back cavity of a micro hot plate structure, which comprises the following steps: taking a wafer loaded with a support film, and loading a layer of photoresist on the front surface of the support film to obtain a wafer loaded with the support film-photoresist; etching the back cavity of the wafer loaded with the support film-photoresist to enable the residual thickness of the wafer to be 30-50 [mu] m so as to obtain an etched wafer; loading a layer of blue film on the front surface of the etched wafer to obtain a wafer loaded with the blue film; and completely etching the wafer loaded with the blue film, and removing the photoresist and the blue film to obtain the blue-film-loaded wafer. The blue film is loaded on the front surface of the film, so that the strength of the front surface film is improved, and the film is prevented from being broken; even if part of the thin film is broken due to stress, the blue film can also prevent the He gas from leaking or falling into the cavity. And meanwhile, the blue film can be quickly removed by utilizing the photoresist, and the prepared film is complete and has no pollution on the front surface.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing and relates to an etching method for the back cavity of a micro hot plate structure. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] MEMS sensors based on micro-hotplate structures typically require etching a back cavity to suspend a supporting thin film on the front side, thus preventing heat loss through diffusion from the substrate silicon. Currently, these supporting thin films are only micrometers thick, making them prone to breakage towards the end of etching due to stress fracture or the impact force generated by the sudden loss of electrostatic force during dechucking. Furthermore, broken film falling onto the chuck can cause equipment downtime and require cavity opening for maintenance. Figure 1 As shown.

[0004] Therefore, the industry urgently needs to solve the problem of support film rupture during the etching process of the back cavity of the micro hot plate structure.

[0005] Some studies have shown that wafers can be stacked on substrates using paraffin wax, but uneven application of paraffin wax can lead to excessive heat and smearing of the photoresist mask; moreover, the paraffin wax is difficult to remove and tends to leave residue.

[0006] Some studies have shown that during the thinning process of the back side of a substrate, a support is attached to the front side of the substrate to protect the front structure. However, the issue of support film rupture during the etching process of the back cavity of a micro hotplate structure has not been addressed. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides an etching method for the back cavity of a micro-hotplate structure. By loading photoresist and a blue film onto the front side of the thin film, the strength of the front film is increased, preventing film breakage; even if part of the film breaks due to stress, the blue film can prevent He gas leakage or falling into the cavity. Simultaneously, the photoresist facilitates rapid removal of the blue film, resulting in an intact film with no contamination on the front side.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for etching the back cavity of a micro-hotplate structure, comprising: Take a wafer loaded with a support film, and load a layer of photoresist on the front side of the support film to obtain a wafer loaded with support film-photoresist. The back cavity of the wafer with the load-supported thin film-photoresist is etched to make the remaining thickness of the wafer 30μm-50μm, so as to obtain the etched wafer. A blue film is loaded onto the front side of the etched wafer to obtain a wafer loaded with a blue film; The wafer loaded with the blue film is completely etched to remove the photoresist and the blue film, thus obtaining the final product.

[0009] In a second aspect, the present invention provides a back cavity structure prepared by the above-described method.

[0010] A third aspect of the present invention provides the application of the above-described back cavity structure in the fabrication of micro hot plates or MEMS sensors.

[0011] Beneficial effects of the present invention (1) This invention increases the strength of the front film by loading photoresist and blue film on the front side of the film, thus preventing the film from cracking. Even if part of the film cracks due to stress, the blue film can prevent He gas from leaking or falling into the chamber. At the same time, the photoresist is used to facilitate the rapid removal of the blue film, and the prepared film is intact and the front side is free of contamination.

[0012] (2) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0013] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0014] Figure 1 This refers to the traditional process flow. Figure 2 The process flow of this invention is as follows: a. 400μm thick wafer, b. support film, c. photoresist, d. blue film.

[0015] Figure 3 The results are for different methods, where A: non-stacked method of Comparative Example 1, B: paraffin stacked method of Comparative Example 2, and C: stacked method of Example 1 of the present invention. Detailed Implementation

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0018] As described in the background art, to address the problem that micron-scale support films are prone to cracking during etching, this invention provides an etching method for the back cavity of a micro-hotplate structure, comprising: Take a wafer loaded with a support film, and load a layer of photoresist on the front side of the support film to obtain a wafer loaded with support film-photoresist. The back cavity of the wafer with the load-supported thin film-photoresist is etched to make the remaining thickness of the wafer 30μm-50μm, so as to obtain the etched wafer. A blue film is loaded onto the front side of the etched wafer to obtain a wafer loaded with a blue film; The wafer loaded with the blue film is completely etched to remove the photoresist and the blue film, thus obtaining the final product.

[0019] In this invention, the blue film and photoresist serve both as a sealing and isolating layer and as a sacrificial layer to protect the support film and prevent it from cracking during etching. Therefore, the thickness of the photoresist affects its adhesion strength to the blue film and its protective effect on the support film. Consequently, this invention has investigated the thickness of the photoresist. In some embodiments, the photoresist thickness is 3-10 μm to effectively load the blue film while better protecting the support film, reducing its cracking probability, and facilitating rapid removal of the blue film.

[0020] Rotation speed and curing temperature affect the thickness and uniformity of photoresist. Therefore, this invention studies the rotation speed and curing temperature during the photoresist coating process. In some embodiments, the specific steps for loading the photoresist include: coating at 3300-3600 rpm, and then curing at 105-110°C for 90-110 seconds. Preferably, the corresponding rotation speed is 3300 rpm; the photoresist is baked and cured at 110°C for 90 seconds to coat a layer of photoresist on the front side of the film using a coating machine.

[0021] Etching gas and etching pressure affect the etching rate and etching effect of the back cavity. Therefore, this invention studies etching gas and etching pressure. In some embodiments, the etching gas is SF6 / C4F8 and the etching pressure is 35-40mt to obtain a better etching effect.

[0022] In some embodiments, the thickness of the blue film is 70μm-100μm. This invention increases the strength of the front-side film by applying the blue film, preventing film breakage; even if part of the film breaks due to stress, the blue film can prevent He gas leakage or falling into the chamber.

[0023] The present invention does not impose any special limitations on the specifications of the wafer. Theoretically, the method of the present invention can be applied to wafers of various specifications. Therefore, in some embodiments, the wafer thickness is 400-775μm.

[0024] In some embodiments, the method for removing the photoresist and blue film involves immersing the wafer in a photoresist remover solution at a preset temperature, wherein the preset temperature is 85-90°C. In this invention, immersing the wafer in a heated photoresist remover solution removes the photoresist while simultaneously removing the blue film, resulting in a complete support film structure.

[0025] This invention does not impose any particular limitation on the type of photoresist remover, as long as it can remove the blue film simultaneously without damaging the supporting film structure. In some embodiments, the photoresist remover is N-methylpyrrolidone to achieve a better removal effect.

[0026] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0027] Example 1 This embodiment uses a 400μm thick wafer as an example to describe the specific process: ① Apply a 7μm thick layer of photoresist to the front side of the film using a coating machine at a rotation speed of 3300 rpm. After coating, bake the photoresist to cure it at 110℃ for 90 seconds.

[0028] ② Place the wafer into a deep silicon etching machine and etch the back cavity to a depth of 350μm. The etching gas is SF6 (sulfur hexafluoride) / C4F8 (octafluorocyclobutane), and the etching pressure is 35mt.

[0029] ② A blue film with a thickness of 80μm is applied to the front of the film using a laminating machine. ④ Place the wafer with the blue film applied back into the etching machine to etch the remaining thickness, using the same etching conditions as in step ②.

[0030] ⑤ Immerse the wafer in a heated resist remover solution to remove the photoresist and the blue film simultaneously, obtaining a complete support film structure; the resist remover solution is heated to 85°C, and the solution composition is NMP (N-methylpyrrolidone). 100%.

[0031] Example 2 This embodiment uses a 400μm thick wafer as an example to describe the specific process: ① Apply a 3μm thick layer of photoresist to the front side of the film using a coating machine at a rotation speed of 3300 rpm. After coating, bake the photoresist to cure it at 110℃ for 90 seconds.

[0032] ② Place the wafer into a deep silicon etching machine and etch the back cavity to a depth of 350μm. The etching gas is SF6 (sulfur hexafluoride) / C4F8 (octafluorocyclobutane), and the etching pressure is 35mt.

[0033] ② A blue film with a thickness of 70μm is applied to the front of the film using a laminating machine.

[0034] ④ Place the wafer with the blue film applied back into the etching machine to etch the remaining thickness, using the same etching conditions as in step ②.

[0035] ⑤ Immerse the wafer in heated resist remover to remove the photoresist and the blue film at the same time, to obtain a complete support film structure; the temperature of the resist remover after heating is 85°C, and the chemical composition of the solution is NMP (N-methylpyrrolidone).

[0036] Example 3 This embodiment uses a 400μm thick wafer as an example to describe the specific process: ① Apply a 10μm thick layer of photoresist to the front side of the film using a coating machine at a rotation speed of 3300 rpm. After coating, bake the photoresist to cure it at 110℃ for 90 seconds.

[0037] ② Place the wafer into a deep silicon etching machine and etch the back cavity to a depth of 350μm. The etching gas is SF6 (sulfur hexafluoride) / C4F8 (octafluorocyclobutane), and the etching pressure is 35mt.

[0038] ② A blue film with a thickness of 100μm is applied to the front of the film using a laminating machine.

[0039] ④ Place the wafer with the blue film applied back into the etching machine to etch the remaining thickness, using the same etching conditions as in step ②.

[0040] ⑤ Immerse the wafer in heated resist remover to remove the photoresist and the blue film at the same time, to obtain a complete support film structure; the temperature of the resist remover after heating is 85°C, and the chemical composition of the solution is NMP (N-methylpyrrolidone).

[0041] Comparative Example 1 Using traditional methods, wafer back cavity etching is performed directly without stacking.

[0042] Comparative Example 2 The difference from Example 1 is that paraffin wax is used instead of the photoresist and blue film of the present invention for wafer back cavity etching, and the film thickness of the paraffin wax sheet is 1 μm.

[0043] Depend on Figure 3 It can be seen that in Comparative Example 1, the non-stacked method resulted in film breakage on the front side; in Comparative Example 2, the paraffin-stacked method resulted in paraffin contamination on the front side, which was difficult to remove. The stacking method of Example 1 of the present invention produces a complete film with no contamination on the front side.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for etching a back cavity of a micro-hotplate structure, characterized in that, The method comprises the following steps: loading a wafer with a supporting film, loading a layer of photoresist on the front surface of the supporting film to obtain a wafer loaded with the supporting film-photoresist; etching the back cavity of the wafer loaded with the supporting film-photoresist to make the remaining thickness of the wafer 30-50 μm to obtain an etched wafer; loading a layer of blue film on the front surface of the etched wafer to obtain a wafer loaded with the blue film; completely etching the wafer loaded with the blue film to remove the photoresist and the blue film.

2. The etching method of the micro-hot plate structure back cavity according to claim 1, wherein, The thickness of the photoresist is 7-9 μm.

3. The etching method of the micro-hot plate structure back cavity according to claim 1, wherein, The specific steps of loading the photoresist include: coating the photoresist at 3300-3600 rpm, and then curing at 105-110 ℃ for 90-110 seconds.

4. The method of claim 1, wherein the micro-hotplate structure back cavity is etched by using a dry etching method. The etching gas is SF6 / C4F8, and the etching pressure is 35-40 mt.

5. The method of claim 1, wherein the micro-hotplate structure back cavity is etched by using a dry etching method. The thickness of the blue film is 70-100 μm.

6. The method of claim 1, wherein the micro-hotplate structure back cavity is etched by using a dry etching method. The thickness of the wafer is 400-775 μm.

7. The method of claim 1, wherein the micro-hotplate structure back cavity is etched by using a dry etching method. The method for removing the photoresist and the blue film is soaking the wafer in a photoresist removing solution at a preset temperature, and the preset temperature is 85-90 ℃.

8. The etching method of the micro-hot plate structure back cavity according to claim 7, wherein, The photoresist removing solution is N-methyl pyrrolidone.

9. The back cavity structure prepared by the method of any one of claims 1-8.

10. The use of the back cavity structure of claim 9 in preparing a micro-hotplate or a MEMS sensor.

Images