Anti-chap cleaning method for MEMS structure
By using EKC270 cleaning solution at low temperature and combining sonic wave cleaning at specific frequency, the problem of cracking on the surface of MEMS structure is solved, achieving efficient cleaning without cracking.
Patent Information
- Application Number
- CN202510454971.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-11
- Publication Date
- 2025-07-15
AI Technical Summary
In the prior art, when using EKC270 to clean the aluminum scandium nitride piezoelectric layer, it is easy to cause cracking of the MEMS structure surface, and the cleaning effect is poor after replacing the cleaning agent.
EKC270 cleaning solution is used to combine sound wave cleaning at 42℃-60℃ with 0.8MHz-5MHz frequency to reduce the cleaning temperature and use sound wave cleaning at a specific frequency to avoid cracking and maintain the cleaning effect.
On the premise of ensuring cleanliness, the surface cracking of the aluminum scandium nitride piezoelectric layer is avoided, which saves cleaning time and improves cleaning efficiency.
Smart Images
Figure CN120308910A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of MEMS manufacturing technology, and particularly to an anti-cracking cleaning method for MEMS structures. Background Art
[0002] Aluminum scandium nitride belongs to aluminum nitride-based materials. Doping with scandium can effectively improve its piezoelectric properties. Therefore, aluminum scandium nitride is often used as the piezoelectric material layer of MEMS devices. After lithography, etching, and resist stripping during the preparation of the above MEMS devices, it is necessary to clean the surface residues.
[0003] EKC270 is one of the series of post-etch residue removers under DuPont Company, mainly used to remove residues after etching or ashing during semiconductor manufacturing. EKC270 usually performs efficient cleaning at a temperature of 70°C - 100°C. When using EKC270 to clean the above-mentioned piezoelectric layer including aluminum scandium nitride, serious surface cracking problems will occur. In order to avoid such cracking problems, in the prior art, the cleaning agent is usually replaced, for example, by using NMP (N-methylpyrrolidone) solvent or DMSO (Dimethyl Sulfoxide) cleaning agent or ultrasonic wave and other methods for cleaning, but the cleaning effect is not good and there are still different degrees of cracking phenomena. Summary of the Invention
[0004] An object of the present invention is to provide an anti-cracking cleaning method for MEMS structures, which can completely avoid surface cracking of the aluminum scandium nitride piezoelectric layer on the premise of ensuring the cleaning effect.
[0005] A further object of the present invention is to save cleaning time and improve cleaning efficiency.
[0006] An embodiment of the present invention provides an anti-cracking cleaning method for MEMS structures. The MEMS structure includes a base layer, a lower film layer, and a piezoelectric layer arranged in sequence. The piezoelectric layer has a preset pattern formed by lithography and dry etching. The material of the piezoelectric layer is aluminum scandium nitride, and the thickness of the piezoelectric layer is any value in the range of 50 nm - 500 nm. The absolute value of the difference in thermal expansion coefficients of two target material layers at a preset temperature is greater than 1.5×10 -6 / °C. The two target material layers are adjacent material layers among the base layer, the lower film layer, and the piezoelectric layer. The cleaning method includes:
[0007] After removing the photoresist, use EKC270 cleaning solution and sound waves within a preset frequency range to perform cleaning simultaneously at the preset temperature. The preset temperature is any value in the range of 42°C - 60°C, and the preset frequency range is 0.8 MHz - 5 MHz.
[0008] Further, the preset frequency range is 0.8 MHz - 3 MHz.
[0009] Further, the impact intensity generated by the megasonic wave in the EKC270 cleaning solution is less than the critical yield strength of the aluminum scandium nitride.
[0010] Further, the cleaning time is any value in the range of 20 min - 60 min.
[0011] Further, the thermal expansion coefficient of the piezoelectric layer is 4.2×10 -6 / °C - 5×10 -6 / °C for any value.
[0012] Further, when the target material layer is the piezoelectric layer and the lower film layer, the thickness of the lower film layer is any value in the range of 100 nm - 1000 nm.
[0013] Further, the material of the lower film layer includes one or more of silicon, silicon dioxide, and silicon nitride.
[0014] Further, when the target material layer is the lower film layer and the base layer, the thickness of the lower film layer is any value in the range of 30 nm - 300 nm.
[0015] Further, the material of the lower film layer includes one or more of aluminum nitride, silicon carbide, and zirconia, and the material of the base layer is silicon.
[0016] Further, when the target material layer is the piezoelectric layer and the lower film layer, the material of the lower film layer is an alloy.
[0017] According to the first aspect of the present invention, the anti-cracking cleaning method of the present application can completely avoid the surface cracking problem of the aluminum scandium nitride piezoelectric layer on the premise of ensuring the cleaning effect, that is, by simply reducing the cleaning temperature and combining with sonic cleaning at a specific frequency, the piezoelectric layer can be prevented from cracking without sacrificing the cleaning effect.
[0018] Further, EKC270 cleaning at a cleaning temperature between 42°C and 60°C and sonic cleaning in the frequency range of 0.8 MHz - 5 MHz can obtain a MEMS structure with high cleanliness and no surface cracking. Compared with the prior art, the cleaning time is saved, indicating that the cleaning method of the present application can save the cleaning time and improve the cleaning efficiency while ensuring the cleanliness and no surface cracking.
[0019] Further, EKC270 cleaning combined with sonic cleaning in the frequency range of 0.8 MHz - 3 MHz between 42°C and 60°C can significantly reduce the cleaning time. Description of the Drawings
[0020] Figure 1 SEM image of the surface of the MEMS structure obtained by the cleaning method in the prior art;
[0021] Figure 2 Flowchart of the anti-cracking cleaning method for the MEMS structure according to an embodiment of the present invention;
[0022] Figure 3 Schematic diagram of the MEMS structure according to Embodiment 1 of the present invention;
[0023] Figure 4 SEM image of the surface of the MEMS structure according to Embodiment 1 of the present invention;
[0024] Figure 5 SEM image of the surface of the MEMS structure of Comparative Example 3;
[0025] Figure 6 SEM image of the surface of the MEMS structure of Comparative Example 7;
[0026] Figure 7 SEM image of the surface of the MEMS structure of Comparative Example 8;
[0027] Figure 8 SEM image of the surface of the MEMS structure of Comparative Example 9.
[0028] Reference Numerals:
[0029] 100 - Target MEMS structure, 10 - Silicon substrate, 20 - Lower film layer, 30 - Piezoelectric layer. Detailed Description of the Embodiments
[0030] To make the above objects, features, and advantages of the present application more apparent and understandable, the following detailed description of the specific embodiments of the present application will be given with reference to the accompanying drawings. Many specific details are set forth in the following description to facilitate a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.
[0031] It should be noted that when a component is referred to as "fixed to" or "disposed on" another component, it can be directly on the other component or there can also be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in the description of this application are only for illustrative purposes and do not represent the only implementation.
[0032] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of this application, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.
[0033] In this application, unless otherwise clearly defined and limited, the first feature may be in direct contact with the second feature "on" or "under" the second feature, or the first feature and the second feature may be in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature has a higher horizontal height than the second feature. The first feature being "below", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature has a lower horizontal height than the second feature.
[0034] Unless otherwise defined, all technical and scientific terms used in the description of this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application are only for the purpose of describing specific implementations and are not intended to limit this application. The term "and / or" used in the description of this application includes any and all combinations of one or more of the related listed items.
[0035] During the process of fabricating a piezoelectric MEMS device (including an aluminum scandium nitride piezoelectric layer deposited on a silicon dioxide substrate), the inventors used EKC270 cleaning solution during the cleaning process of surface residues after lithography, etching and removal of photoresist after depositing the piezoelectric. In order to increase the chemical reaction rate and accelerate the dissolution and stripping of contaminants, a cleaning temperature of 70°C - 100°C was adopted to enhance the removal ability of stubborn residues (such as photoresist after high-temperature baking). As Figure 1 shown, this cleaning method has caused serious cracking problems on the surface of the piezoelectric layer. When such serious cracking problems occur on the surface of the piezoelectric layer, those skilled in the art usually skip the cleaning step of this cleaning solution or switch to other cleaning methods.
[0036] In order to continue to use the cleaning liquid EKC270 with better cleaning effect, the inventor accidentally found that by reducing the cleaning temperature in combination with megasonic cleaning, while meeting the cleaning requirements, the problem of surface cracking of the piezoelectric layer can be completely avoided. Based on the basic knowledge in this field, the generation of cracks is generally caused by factors such as large stress during the deposition process and residual stress during the etching process. Therefore, those skilled in the art generally would not think of improving the problem of piezoelectric layer cracking by reducing the cleaning temperature of EKC270. And the reduction of temperature will affect the diffusion between molecules in the cleaning liquid, which is adverse to the cleaning effect. This further makes those skilled in the art not prevent the surface cracking of the piezoelectric layer from the direction of reducing the cleaning temperature. The accidental discovery of the inventor breaks through the existing technical prejudice and achieves excellent effects of cleaning and preventing surface cracking through simple technical means.
[0037] This application cleans a MEMS structure including a lower film layer and a piezoelectric layer arranged in sequence. Here, the MEMS structure can be understood as a structure formed during the preparation of a MEMS device, which may not be the final product of the MEMS device. As long as this preparation process involves a structure including a lower film layer and a piezoelectric layer, after the materials of the lower film layer and the piezoelectric layer are deposited in sequence, a required preset pattern is formed on the piezoelectric layer through photolithography and etching methods. Here, the etching is dry etching, such as common plasma etching. The material of the piezoelectric layer is aluminum scandium nitride (AlScN). The absolute value of the difference in the coefficient of thermal expansion of the two target material layers at the preset temperature is greater than 1.5×10 -6 / °C, the thickness of the piezoelectric layer is any value in the range of 50 nm - 500 nm. For example, the thickness of the piezoelectric layer is 50 nm, 70 nm, 100 nm, 140 nm, 180 nm, 200 nm, 230 nm, 260 nm, 300 nm, 350 nm, 400 nm, 420 nm, 450 nm or 500 nm, or any other value in the range of 50 nm - 500 nm, which is not limited here. The two target material layers are adjacent material layers among the base layer, the lower film layer and the piezoelectric layer, that is, the absolute value of the difference in the coefficient of thermal expansion of the lower film layer and the piezoelectric layer at the preset temperature is greater than 1.5×10 -6 / °C, or the absolute value of the difference in the coefficient of thermal expansion of the lower film layer and the base layer at the preset temperature is greater than 1.5×10 -6 / °C. Here, the preset temperature is the cleaning temperature in the following text.
[0038] Figure 2 It is a flowchart of an anti-cracking cleaning method for a MEMS structure according to an embodiment of the present invention. As Figure 2 shown, in one embodiment, the anti-cracking cleaning method for a MEMS structure includes:
[0039] Step S100, after removing the photoresist, perform cleaning simultaneously with EKC270 cleaning solution and acoustic waves within a preset frequency range at a preset temperature, where the preset temperature is any value in the range of 42°C - 60°C, and the preset frequency range is 0.8 MHz - 5 MHz.
[0040] The preset temperature can be 42°C, 45°C, 50°C, 52°C, 55°C or 60°C, and the preset temperature can also be any other value in the range of 42°C - 60°C, which is not limited here. The preset frequency is 0.8 MHz, 1 MHz, 1.5 MHz, 1.8 MHz, 2 MHz, 2.2 MHz, 2.5 MHz, 3 MHz, 3.5 MHz, 3.8 MHz, 4 MHz, 4.2 MHz, 4.5 MHz or 5 MHz, and the preset frequency can also be any other value in the range of 0.8 MHz - 5 MHz, which is not limited here.
[0041] After obtaining the above cleaning solution, the inventor studied its mechanism of action and found that the reason for the surface cracking of the piezoelectric layer in the above MEMS structure is that the difference in thermal expansion amplitude between the piezoelectric layer and the lower film layer combined with the bottom surface of the piezoelectric layer or between the lower film layer and the substrate layer causes the thermal stress to exceed the critical yield strength of the piezoelectric layer, resulting in the breaking of Sc-N, Al-N bonds or the chemical bonds of the lower film layer material and lattice collapse. By reducing the cleaning temperature of EKC270, the thermal stress can be alleviated, so that the thermal stress difference between the piezoelectric layer and the lower film layer or between the lower film layer and the substrate layer will not cause lattice collapse of the piezoelectric layer or the lower film layer, thereby avoiding the problem of piezoelectric layer cracking. Further, by simultaneously cleaning with acoustic waves of a specific frequency when cleaning with EKC270, the high-frequency acoustic waves can shorten the bubble growth time, effectively reduce the cavitation intensity, and the impact pressure generated by the acoustic waves in the EKC270 cleaning solution at this frequency is less than the critical yield strength of aluminum scandium nitride, so it will not cause lattice collapse of the piezoelectric layer. At the same time, the acoustic waves can accelerate the diffusion of EKC270 molecules, improve the chemical dissolution efficiency, increase the contact area of the EKC270 cleaning solution with photolithography and etching residues, improve the uniformity of cleaning, and can also promote the faster detachment of dissolved pollutants from the surface, reducing the risk of secondary deposition. The cavitation bubbles generated by acoustic waves in the range of 0.8 MHz - 5 MHz are smaller and will not generate violent shock waves or microjets, but can still provide micro-perturbations and surface shear forces, which helps to remove etching residues. The stable cavitation effect can effectively break the adhesion force between pollutants and the substrate, making it easier for the EKC270 cleaning solution to dissolve residual pollutants at 42°C - 60°C.
[0042] Based on the above principle, the anti-cracking cleaning method of the present application can completely avoid the surface cracking problem of the aluminum scandium nitride piezoelectric layer on the premise of ensuring the cleaning effect, that is, by simply reducing the cleaning temperature and combining with acoustic wave cleaning at a specific frequency, the cracking of the piezoelectric layer can be avoided without sacrificing the cleaning effect.
[0043] Furthermore, the experimental data also show that when reducing the cleaning temperature of the EKC270 cleaning solution and combining with acoustic wave cleaning at 0.8 MHz - 5 MHz, the cleaning time can be effectively saved and the cleaning efficiency can be improved.
[0044] In a further embodiment, the preset frequency range is 0.8 MHz - 3 MHz. For example, the preset frequencies are 0.8 MHz, 1.2 MHz, 1.5 MHz, 1.7 MHz, 2 MHz, 2.3 MHz, 2.6 MHz or 3 MHz. The preset frequency can also be any other value within 0.8 MHz - 3 MHz, which is not limited here. The cleaning time is any value within 20 min - 60 min. For example, the cleaning time is 20 min, 25 min, 27 min, 30 min, 35 min, 40 min, 42 min, 45 min, 50 min, 52 min, 56 min or 60 min. The cleaning time can also be any other value within 20 min - 60 min, which is not limited here.
[0045] In one embodiment, the coefficient of thermal expansion of the piezoelectric layer is 4.2×10 -6 / ℃ - 5×10 -6 / ℃. For example, the coefficient of thermal expansion of the piezoelectric layer is 4.2×10 -6 / ℃, 4.3×10 -6 / ℃, 4.5×10 -6 / ℃, 4.6×10 -6 / ℃, 4.8×10 -6 / ℃ or 5.0×10 -6 / ℃. The coefficient of thermal expansion of the piezoelectric layer can also be any other value within 4.2×10 -6 / ℃ - 5×10 -6 / ℃, which is not limited here.
[0046] In one embodiment, when the target material layer is a piezoelectric layer and a lower film layer, the thickness of the lower film layer is any value in the range of 100 nm to 1000 nm. For example, the thickness of the lower film layer is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 760 nm, 800 nm, 830 nm, 850 nm, 900 nm, 950 nm or 1000 nm, or any other value in the range of 100 nm to 1000 nm, which is not limited herein. The material of the lower film layer includes one or more of silicon, silicon dioxide and silicon nitride. At this time, the MEMS structure may only include a piezoelectric layer and a lower film layer. When a substrate layer is included, the material of the substrate layer is silicon.
[0047] In another embodiment, when the target material layer is a piezoelectric layer and a lower film layer, the material of the lower film layer is an alloy, such as copper-aluminum alloy, copper, aluminum, silver, bronze, etc.
[0048] In one embodiment, when the target material layer is a lower film layer and a substrate layer, the thickness of the lower film layer is any value in the range of 30 nm to 300 nm. For example, the thickness of the lower film layer is 30 nm, 35 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 180 nm, 200 nm, 240 nm, 250 nm, 280 nm, or 300 nm, or any other value in the range of 50 nm to 500 nm, which is not limited herein. The material of the lower film layer includes one or more of aluminum nitride, silicon carbide and zirconia, and the material of the substrate layer is silicon.
[0049] When the cause of the crack is the difference value of the thermal expansion coefficients of the lower film layer and the substrate layer, when the thickness of the lower film layer is relatively thick, it can digest this crack by itself without transmitting to the surface of the lower film layer, and thus will not cause cracks in the piezoelectric layer. However, in the preparation process of some devices, the thickness of the lower film layer is limited. When the thickness of the lower film layer is within a certain range, the crack of the lower film layer will extend to its surface and cause cracks in the piezoelectric layer. For the cracks in this case, the cleaning method of the present application can also avoid cracks in the piezoelectric layer.
[0050] Embodiment 1
[0051] Figure 3 It is a schematic diagram of the MEMS structure according to Embodiment 1 of the present invention. The target MEMS structure 100 is cleaned. As Figure 3 shown, the target MEMS structure 100 includes a silicon substrate 10, a lower film layer 20 and a piezoelectric layer 30 arranged in sequence. The material of the lower film layer 20 is silicon dioxide, the thickness is 200 nm, and the material of the piezoelectric layer 30 is scandium aluminum scandium nitride with a scandium doping amount of 20%, and the corresponding thermal expansion coefficient is 4.6×10 -6 / °C, with a thickness of 300 nm. During photolithography, AZ5214 photoresist, an i-line (356 nm) ultraviolet light source, and AZ 300MIF developer were used. Plasma etching of the piezoelectric layer 30 was carried out using Cl2 + BCl3 + Ar etching gas and stopped at the upper surface of the lower film layer 20. O2 plasma ashing was used to remove the photoresist, and the photoresist was removed for 2 minutes at a temperature of 50 °C, a power of 200 W, and an oxygen flow rate of 300 sccm.
[0052] During cleaning, the cleaning temperature was 50 °C, the acoustic wave frequency was 2 MHz, and the cleaning time was 25 minutes.
[0053] Example 2
[0054] The difference between Example 2 and Example 1 is only that the cleaning temperature is 42 °C and the cleaning time is 30 minutes.
[0055] Example 3
[0056] The difference between Example 3 and Example 1 is only that the cleaning temperature is 60 °C and the cleaning time is 27 minutes.
[0057] Example 4
[0058] The difference between Example 4 and Example 1 is only that the acoustic wave frequency is 0.8 MHz and the cleaning time is 28 minutes.
[0059] Example 5
[0060] The difference between Example 5 and Example 1 is only that the acoustic wave frequency is 2.5 MHz and the cleaning time is 20 minutes.
[0061] Example 6
[0062] The difference between Example 6 and Example 1 is only that the acoustic wave frequency is 3 MHz and the cleaning time is 22 minutes.
[0063] Example 7
[0064] The difference between Example 7 and Example 1 is only that the acoustic wave frequency is 3.2 MHz and the cleaning time is 32 minutes.
[0065] Example 8
[0066] The difference between Example 8 and Example 1 is only that the acoustic wave frequency is 4 MHz and the cleaning time is 40 minutes.
[0067] Example 9
[0068] The difference between Example 9 and Example 1 is only that the acoustic wave frequency is 5 MHz and the cleaning time is 42 minutes.
[0069] Example 10
[0070] Example 10 is only different from Example 1 in that the material of the lower film layer is aluminum nitride, the thickness of the lower film layer is 200 mm, and the cleaning time is 23 minutes.
[0071] Comparative Example 1
[0072] Comparative Example 1 is only different from Example 1 in that the cleaning temperature is 35 °C and the cleaning time is 80 minutes.
[0073] Comparative Example 2
[0074] Comparative Example 2 is only different from Example 1 in that the cleaning temperature is 62 °C and the cleaning time is 40 minutes.
[0075] Comparative Example 3
[0076] Comparative Example 3 is only different from Example 1 in that the cleaning temperature is 75 °C and the cleaning time is 30 minutes.
[0077] Comparative Example 4
[0078] Comparative Example 4 is only different from Example 1 in that the acoustic wave frequency is 0.6 MHz and the cleaning time is 60 minutes.
[0079] Comparative Example 5
[0080] Comparative Example 5 is only different from Example 1 in that the acoustic wave frequency is 6 MHz and the cleaning time is 50 minutes.
[0081] Comparative Example 6
[0082] Comparative Example 6 is only different from Example 1 in that only the EKC270 cleaning solution is used for cleaning, the cleaning temperature is 75 °C, and the cleaning time is 45 minutes.
[0083] Comparative Example 7
[0084] Comparative Example 7 is only different from Example 1 in that after using the EKC270 cleaning solution for 15 minutes at the cleaning temperature, megasonic waves with an acoustic wave frequency of 2 MHz are combined with the UPW + 0.1% Triton X-100 cleaning solution and cleaned for 10 minutes at a cleaning temperature of 50 °C.
[0085] Comparative Example 8
[0086] Comparative Example 8 is only different from Example 10 in that only the EKC270 cleaning solution is used for cleaning, the cleaning temperature is 75 °C, and the cleaning time is 43 minutes.
[0087] Comparative Example 9
[0088] The difference between Comparative Example 8 and Example 10 is only that after cleaning with EKC270 cleaning solution at a cleaning temperature of 50°C for 15 minutes, megasonic waves with a sonic frequency of 2 MHz are combined with UPW + 0.1% Triton X-100 cleaning solution, and the cleaning is carried out at a cleaning temperature of 50°C for 10 minutes.
[0089] Experimental data of the above examples and comparative examples were collected. The surface of the piezoelectric layer was observed by scanning electron microscopy to obtain the surface condition of the piezoelectric layer, and the contact angles of the piezoelectric layer and the lower film layer were measured to test the surface cleanliness. The experimental results are shown in Table 1 below.
[0090] Table 1
[0091]
[0092] Figure 4 It is a scanning electron micrograph of the surface of the MEMS structure according to Example 1 of the present invention. Figure 5 It is a scanning electron micrograph of the surface of the MEMS structure of Comparative Example 3. Figure 6 It is a scanning electron micrograph of the surface of the MEMS structure of Comparative Example 7. As Figure 4 shown, the surface of the MEMS structure of Example 1 of the present application (i.e., the piezoelectric layer side) has no cracks at all, with good cleaning effect and extremely short cleaning time. There are no cracks on the surface of the MEMS structure in Comparative Example 1, but the cleanliness is still very low when the cleaning duration reaches 80 minutes, and the cleaning efficiency is low, not meeting the cleaning requirements. As Figure 5 and Figure 7 shown, there are local moderate cracks on the surface of the MEMS structure in Comparative Example 3 and Comparative Example 7. For Comparative Example 6, that is, Figure 1 shown, severe cracks appear on the surface of the MEMS structure obtained by the cleaning method of the prior art.
[0093] Figure 7 It is a scanning electron micrograph of the surface of the MEMS structure of Comparative Example 8. Figure 8 It is a scanning electron micrograph of the surface of the MEMS structure of Comparative Example 9. As Figure 7 and 8 shown, severe cracks appear on the MEMS structure of Comparative Example 8 and Comparative Example 9 when viewed from the light-transmitting piezoelectric layer side.
[0094] It should be noted that Comparative Examples 2 to 6 need a cleaning duration of more than 30 minutes to achieve the required cleanliness (****), and different degrees of cracks will appear when the cleaning time reaches about 20 minutes. For example, Comparative Example 3 shows moderate cracks as Figure 5 shown when the cleaning time is 45 minutes. As Figure 1 and Figure 7As shown, for Comparative Example 6, the required cleanliness can be achieved when cleaning for 45 minutes, and for Comparative Example 8, when cleaning for about 43 minutes. However, severe cracks occurred in both cases. As Figure 6 shown, for Comparative Example 7, the cleanliness requirement can be met when the total cleaning duration is 25 minutes, but moderate cracks occurred. As Figure 8 shown, for Comparative Example 9, the cleanliness requirement can be met when the total cleaning duration is 25 minutes, but relatively severe cracks occurred.
[0095] It can be seen from this that in the prior art, when cleaning EKC270 at high temperature or using the method of cleaning with EKC270 and megasonic waves in sequence, there will be crack phenomena.
[0096] The experimental data of Examples 1 to 9 show that when cleaning EKC270 at a cleaning temperature between 42°C and 60°C and sonic cleaning in the frequency range of 0.8 MHz to 5 MHz, a MEMS structure with high cleanliness and no cracks on the surface can be obtained. Compared with Comparative Example 6 (i.e., the prior art), the cleaning time is also saved. This shows that the cleaning method of the present application can save cleaning time and improve cleaning efficiency while ensuring cleanliness and no cracks on the surface.
[0097] In Examples 7 to 9, the sonic frequencies are 3.2 MHz, 4 MHz, and 5 MHz respectively, which are in the range of 3 MHz to 5 MHz. They also have good cleanliness and ensure no cracks on the surface. However, the cleaning time is significantly increased compared with Examples 1 to 8 in the frequency range of 0.8 MHz to 3 MHz. This shows that EKC270 cleaning combined with sonic cleaning in the frequency range of 0.8 MHz to 3 MHz between 42°C and 60°C can significantly reduce the cleaning time and control the cleaning time within 30 minutes.
[0098] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.
Claims
1. A method for preventing cracking during cleaning of a MEMS structure, characterized in that, The MEMS structure includes a base layer, a lower film layer, and a piezoelectric layer arranged in sequence. The piezoelectric layer has a preset pattern formed by photolithography and dry etching. The material of the piezoelectric layer is aluminum scandium nitride, and the thickness of the piezoelectric layer is any value in the range of 50 nm to 500 nm. The absolute value of the difference in the coefficient of thermal expansion of two target material layers at a preset temperature is greater than 1.5×10 -6 / °C. The two target material layers are adjacent material layers among the base layer, the lower film layer, and the piezoelectric layer. The cleaning method includes: After removing the photoresist, cleaning is simultaneously performed using an EKC270 cleaning solution and acoustic waves within a preset frequency range at the preset temperature, where the preset temperature is any value within 42°C - 60°C, and the preset frequency range is 0.8 MHz - 5 MHz.
2. The anti-cracking cleaning method for the MEMS structure according to claim 1, wherein The preset frequency range is 0.8 MHz - 3 MHz.
3. The anti-cracking cleaning method for the MEMS structure according to claim 1, characterized in that, The impact intensity generated by the megasonic waves in the EKC270 cleaning solution is less than the critical yield strength of the aluminum scandium nitride.
4. The anti-cracking cleaning method of the MEMS structure according to claim 2, characterized in that, The cleaning time is any value within 20 min - 60 min.
5. The anti-cracking cleaning method for the MEMS structure according to claim 1, wherein, The thermal expansion coefficient of the piezoelectric layer is 4.2×10 -6 / °C - 5×10 -6 / °C, where the value can be any one within this range.
6. The anti-cracking cleaning method of the MEMS structure according to any one of claims 1-5, characterized in that, When the target material layer is the piezoelectric layer and the lower film layer, the thickness of the lower film layer is any value within 100 nm - 1000 nm.
7. The anti-cracking cleaning method of the MEMS structure according to claim 6, characterized in that, The material of the lower film layer includes one or more of silicon, silicon dioxide, and silicon nitride.
8. The anti-cracking cleaning method for the MEMS structure according to any one of claims 1-5, characterized in that, When the target material layer is the lower film layer and the substrate layer, the thickness of the lower film layer is any value within 30 nm - 300 nm.
9. The anti-cracking cleaning method for the MEMS structure according to claim 8, characterized in that, The material of the lower film layer includes one or more of aluminum nitride, silicon carbide, and zirconia, and the material of the substrate layer is silicon.
10. The anti-cracking cleaning method for the MEMS structure according to any one of claims 1-5, characterized in that, When the target material layer is the piezoelectric layer and the lower film layer, the material of the lower film layer is an alloy.