Resonator and method of forming the same, electronic device

Abstract

The application discloses a resonator and a forming method thereof, and an electronic device. The forming method of the resonator comprises the following steps: forming an acoustic mirror structure on a substrate; forming a bottom electrode on the acoustic mirror structure; forming a piezoelectric layer on the bottom electrode; forming a top electrode on the piezoelectric layer; and further comprising the following steps: forming a patterned load layer below the bottom electrode, below the piezoelectric layer, below the top electrode, above the top electrode or inside each film layer, which specifically comprises the following steps: forming a patterned photoresist layer, the thickness of the photoresist layer is less than a preset thickness threshold; depositing the patterned load layer; and removing the photoresist layer. The application guarantees the pattern precision of the patterned load layer by controlling the thickness of the photoresist layer, the processing result has better uniformity and repeatability, has a favorable influence on the performance of the resonator, and improves the device yield.

Description

Technical Field

[0001] This invention relates to the field of microelectronics technology, specifically to a resonator and its formation method, as well as an electronic device. Background Technology

[0002] The rapid trend towards miniaturization and high performance in communication equipment in recent years has presented greater challenges to radio frequency (RF) front-ends. In a typical structure of a common filter, there is an inductor and multiple resonators (usually called series resonators) between the input and output terminals. Multiple branches (usually called parallel branches) between the connection points of each series resonator and the ground terminal are each equipped with a resonator (usually called a parallel resonator) and an inductor. A mass load layer is added to each parallel resonator, causing a difference in frequency between the parallel and series resonators, thus forming the passband of the filter.

[0003] Patterning the load layer increases the frequency freedom of each resonator in the filter design, thereby improving filter performance. The patterned load layer needs to have good uniformity and repeatability. However, in existing technologies, excessively thick photoresist leads to low yield of the patterned load layer, significantly impacting the final device performance. Summary of the Invention

[0004] In view of this, the present invention proposes a resonator with a high-precision patterned load layer, a method for manufacturing the same, and an electronic device including the resonator.

[0005] The first aspect of this invention provides a method for forming a resonator, comprising: forming an acoustic mirror structure on a substrate; forming a bottom electrode on the acoustic mirror structure; forming a piezoelectric layer on the bottom electrode; forming a top electrode on the piezoelectric layer; and optionally forming a passivation layer on the top electrode. This invention is primarily illustrated using the case with a passivation layer as an example, but is not limited to this in implementation. Whether or not a passivation layer is present is within the scope of protection of this invention. The method further includes: forming a patterned load layer below the bottom electrode, below the piezoelectric layer, below the top electrode, below the passivation layer, above the passivation layer, or inside each film layer. This step specifically includes: forming a patterned photoresist layer, the thickness of which is less than a preset thickness threshold; depositing the patterned load layer; and removing the photoresist layer.

[0006] Optionally, the load layer is formed below, above, or inside the passivation layer.

[0007] Optionally, the preset thickness threshold is 2.8 to 3.3 micrometers.

[0008] Optionally, the process conditions in the step of forming a patterned photoresist layer on the top electrode are as follows: the photoresist viscosity is 10-120 cp; further, the exposure time can be 10-14 s; the coating speed can be 4000-5000 rpm / s; further still, the PEB temperature can be 90-120℃; and the PEB time can be 90-120 s.

[0009] Optionally, the graphical load layer includes multiple uniformly distributed load islands of the same shape and size.

[0010] Optionally, the load island is a regular polygon or a circle.

[0011] Optionally, the plurality of load islands are arranged in a planar periodic pattern.

[0012] Optionally, the graphical load layer includes multiple concentric circular rings or multiple concentric polygonal rings as load rings.

[0013] Optionally, the graphical load layer is an irregular shape.

[0014] Optionally, the photoresist is a negative photoresist.

[0015] A second aspect of the present invention provides a resonator, which is manufactured by the resonator forming method disclosed in the present invention.

[0016] A third aspect of the present invention provides an electronic device including the resonator disclosed herein.

[0017] According to the technical solution of the present invention, the pattern accuracy of the patterned load layer is ensured by controlling the thickness of the photoresist layer, and the processing result has good uniformity and repeatability, which has a beneficial effect on the resonator performance and improves the device yield. Attached Figure Description

[0018] For illustrative and not limiting purposes, the invention will now be described with reference to preferred embodiments thereof, particularly the accompanying drawings, in which:

[0019] Figure 1 Micrographs of a graphic load layer with a ring-shaped design that shows signs of peeling;

[0020] Figure 2 A graphic image of a load layer designed to depict dots that exhibit non-uniformity;

[0021] Figure 3 This is a schematic diagram comparing the performance of different batches of samples processed under thick adhesive conditions.

[0022] Figure 4 This is a schematic diagram of the photoresist morphology when the photoresist thickness is 2.2 micrometers;

[0023] Figure 5 A micrograph of a patterned load layer with a ring-shaped design obtained by the method for forming a resonator according to an embodiment of the present invention;

[0024] Figure 6 A micrograph of a patterned load layer with a dotted design obtained by the method for forming a resonator according to an embodiment of the present invention.

[0025] Figure 7 This is a schematic diagram comparing the performance of different batches of samples processed under thin-film conditions according to an embodiment of the present invention.

[0026] Figure 8 This is a top view schematic diagram of the first patterned load layer in the resonator according to an embodiment of the present invention;

[0027] Figure 9 This is a top view schematic diagram of the second type of patterned load layer in the resonator according to an embodiment of the present invention;

[0028] Figure 10 This is a top view schematic diagram of the third type of patterned load layer in the resonator according to an embodiment of the present invention;

[0029] Figure 11 This is a top view schematic diagram of the fourth type of patterned load layer in the resonator according to an embodiment of the present invention;

[0030] Figures 12a to 12h This is a schematic diagram illustrating the process of forming a resonator according to an embodiment of the present invention. Detailed Implementation

[0031] In this embodiment of the invention, by patterning the load layer, the frequency freedom of each resonator in the filter design is increased, thereby improving the filter's performance. In other words, changing the area ratio of the patterned load layer (MassLoad, ML) of different resonators in an FBAR filter allows for more flexible adjustment of the frequency of each resonator, and this method simplifies the resonator fabrication process, thus saving costs. For example, in a filter composed of n resonators, using conventional processes, if m (m≤n) resonators of different frequencies need to be fabricated, m photolithography steps are required, resulting in high costs. However, with the patterned load layer process, by setting different duty cycles on different resonators, multiple resonators of different frequencies can be fabricated in a single photolithography and thin film deposition process, thereby simplifying the fabrication process and reducing the fabrication cost of the FBAR filter chip.

[0032] Furthermore, considering that improving product performance using a graphical load layer requires achieving frequency differences between different resonators within the same filter, it is necessary to minimize the frequency differences between each resonator while maintaining good process uniformity. Figure 12h It is known that the patterned load layer 60 can be selectively fabricated above the top electrode, and under preferred conditions, both the patterned load layer and the top electrode are metallic Mo. Therefore, in this embodiment of the invention, a lift-off process is employed, along with the use of negative photoresist to achieve this objective. This avoids excessive etching of the top electrode using traditional etching processes. Because the thickness of the photoresist is related to the minimum linewidth obtained, this embodiment of the invention proposes a relationship between the uniformity of the patterned load layer and the thickness of the negative photoresist, and outlines the conditions that must be met when using negative photoresist. Furthermore, the shape of the patterned load layer used in different products may differ, and the shape of the patterned load layer used in different resonators of the same filter may also differ. Different shapes of load layers require different thicknesses of negative photoresist. Based on this, this embodiment of the invention proposes a relationship between the thickness of different shaped load layers and the thickness of the negative photoresist.

[0033] Experience shows that when the photoresist thickness is large and the fabricated linewidth is small, the uniformity of the photoresist linewidth after exposure is poor, and peeling is more likely to occur after development. This limits the range of shapes that can be selected for the patterned load layer. For products using the lift-off process, the spacing after exposure determines the actual linewidth of the ML, and the linewidth after exposure determines the spacing of the actual ML shape. Therefore, it is necessary to study the relationship between photoresist thickness and different patterned load layer shapes.

[0034] If the patterned load layer is designed in a ring shape, and the thickness of the negative photoresist is 5.5 micrometers, the resulting load layer is prone to peeling off, such as... Figure 1 As shown, this is because the resulting photoresist after exposure is ring-shaped, and the contact area between the photoresist and the underlying Mo metal is small. Therefore, when the linewidth of the photoresist is less than 5 micrometers, the photoresist is prone to peeling off. Thus, this thickness of negative photoresist affects the use of ring-shaped or similar ring-shaped ML processes. If it is a dot-shaped patterned load layer, when the thickness of the negative photoresist is 5.5 micrometers, the uniformity of each point is not ideal, as shown in Figure 2. In this case, the shape of the negative photoresist after exposure is mesh-like, so it is not easy to peel off, but... Figure 2 As can be seen, the shape uniformity of the point-like ML at this time is relatively poor, which will affect the uniformity of the final data.

[0035] Under this adhesive thickness condition, the obtained small frequency difference data were analyzed to obtain... Figure 3 The data shown is in Figure 3In the diagram, the vertical axis represents (actual frequency deviation - theoretical frequency deviation) / theoretical frequency deviation, and the horizontal axis represents different duty cycles. Figure 3 As can be seen, under the same conditions, there are significant differences between the actual and theoretical frequency differences obtained from different batches of samples (i.e., the samples represented by the dashed lines and the samples represented by the solid lines). This indicates that there are problems with uniformity and poor repeatability under this photoresist thickness condition, making it unsuitable for mass production. Furthermore, for each of these two batches of products, the actual frequency difference obtained differs significantly from the required frequency difference. Based on this, it is necessary to reduce the thickness of the photoresist to meet the requirements of the patterned load layer process.

[0036] The resonator formation method according to embodiments of the present invention may include the following aspects, and the formation order of each layer can be adjusted according to actual needs: forming an acoustic mirror structure on a substrate; forming a bottom electrode on the acoustic mirror structure; forming a piezoelectric layer on the bottom electrode; forming a top electrode on the piezoelectric layer; forming a patterned photoresist layer on the top electrode, the thickness of the photoresist layer being less than a preset thickness threshold; depositing a patterned load layer; removing the photoresist layer; and forming a passivation layer on the current semiconductor structure. The thickness threshold can be 3 micrometers. This description uses the example of the load layer being formed on the top electrode; in implementation, the load layer can also be located at any position in the thickness direction of the resonator.

[0037] A preferred embodiment of the present invention is a fabrication scheme using negative photoresist to meet the process conditions. Since both the dot-shaped photoresist matrix (ML) and the top electrode are made of metallic Mo, this process can only be fabricated using lift-off. Therefore, in this embodiment, negative photoresist is used to achieve this objective. Because the thickness of the photoresist is related to the minimum linewidth obtained, this embodiment proposes the relationship between the uniformity of the dot-shaped process and the thickness of the negative photoresist, as well as the conditions that the negative photoresist must meet when using dot-shaped MLs. Furthermore, to meet usage requirements, different products may use different shapes of dot-shaped MLs, and different resonators of the same filter may also use different shapes of dot-shaped MLs. Different shapes of MLs require different thicknesses of negative photoresist. Based on this, this embodiment proposes the relationship between different shapes of MLs and the thickness of the negative photoresist.

[0038] Since there is a certain correlation between the thickness and viscosity of negative photoresist, that is, the lower the viscosity of the photoresist, the thinner the photoresist will be under the same preparation conditions, which is more conducive to the uniformity of the final photoresist linewidth. Therefore, in the resonator formation method of this invention, the process conditions in the step of forming a patterned photoresist layer on the top electrode can be as follows: photoresist viscosity 10-120 cp; exposure time 10-14 s (too long an exposure time will cause overexposure and pattern peeling, too short an exposure time will cause underexposure and incomplete patterning); coating speed 4000-5000 rpm / s (too low a speed will not be able to coat the photoresist evenly, too high a speed may cause the photoresist to be thrown off); PEB (Post Exposure Bake) temperature 90-120℃; PEB duration 90-120 s. The purpose of PEB operation is to reduce the influence of standing wave effect and to make the chemical reaction more complete. If the temperature or time is not suitable, the final pattern morphology will be unsatisfactory. Under these process conditions, negative photoresist with a thickness of less than 3 micrometers can be obtained.

[0039] Figure 4 The image shows the morphology of the photoresist when the thickness is 2.2 micrometers. The photoresist is coated relatively evenly.

[0040] When the photoresist thickness is less than 3 micrometers, for example, when the photoresist thickness is 2.2 micrometers, a ring-shaped patterned load layer fabrication experiment was conducted, and the results are as follows: Figure 5 As shown in the image, the pattern shows no peeling and the shape remains intact, indicating a good processing result.

[0041] When the photoresist thickness is less than 3 micrometers, for example, when the photoresist thickness is 2.2 micrometers, experiments were conducted on the fabrication of a patterned load layer with a dotted design. The results are as follows: Figure 6 As shown, the dots are evenly distributed in a square grid, and each dot has a uniform shape, is intact without peeling, and has a good processing effect.

[0042] Samples from different batches were prepared with a photoresist thickness of 2.2 micrometers, and the differences between actual frequency differences and theoretical values ​​were compared. Figure 7 In the diagram, the vertical axis represents (actual frequency deviation - theoretical frequency deviation) / theoretical frequency deviation, and the horizontal axis represents different duty cycles. Figure 7 It can be seen that the solid and dashed test curves of the two samples almost overlap, which means that the difference between the actual frequency difference and the theoretical value of different batches of samples prepared under this thin adhesive condition is small. This indicates that under this adhesive thickness condition, due to its good uniformity and repeatability, it can be used in mass production.

[0043] As can be seen from the above, by controlling the thickness of the photoresist layer, the pattern accuracy of the patterned load layer is ensured, the processing results have good uniformity and repeatability, which has a positive impact on the resonator performance and improves the device yield.

[0044] In the resonator formation method of this invention, the patterned load layer may include multiple uniformly distributed load islands of the same shape and size. The load islands may be regular polygons or circles, etc. The multiple load islands may be arranged in a planar, periodic pattern. Examples of embodiments are provided. Figure 8 and Figure 9 As shown.

[0045] Figure 8 As shown, the regular pentagonal frame represents the effective area of ​​the resonator, and multiple squares arranged in a grid pattern represent multiple load islands. The distance between the center points of two adjacent square load islands is d1, and the side length of a single square load island is d2. The duty cycle r = (d2 / d1) can be adjusted by changing the ratio of d2 / d1. 2 Finally, the frequency of the resonator is adjusted.

[0046] Figure 9 As shown, the regular pentagonal frame represents the effective area of ​​the resonator, and the multiple dots arranged in a close-packed equilateral triangular plane represent multiple load islands. With a fixed dot spacing, a larger diameter results in a larger duty cycle; conversely, with a fixed dot diameter, a larger spacing results in a smaller duty cycle. Therefore, the duty cycle can be adjusted by changing the dot diameter and spacing, ultimately regulating the resonator's frequency.

[0047] In the resonator formation method of this invention, the patterned load layer may include multiple concentric circular rings or multiple concentric polygonal ring load rings. Examples of embodiments are provided. Figure 10 and Figure 11 As shown.

[0048] Figure 10 As shown, the circular outer frame represents the effective area of ​​the resonator, and the multiple shaded concentric rings represent multiple load rings. With a fixed ring spacing, a larger ring width results in a larger duty cycle; conversely, with a fixed ring width, a larger ring spacing results in a smaller duty cycle. Therefore, the duty cycle can be adjusted by changing the ring width and spacing, ultimately regulating the resonator's frequency.

[0049] Figure 11As shown, the regular pentagonal frame represents the effective area of ​​the resonator, and the multiple shaded concentric pentagonal rings represent multiple load rings. With a fixed spacing between the pentagonal rings, a larger ring width results in a larger duty cycle; conversely, with a fixed ring width, a larger spacing between the rings results in a smaller duty cycle. Therefore, the duty cycle can be adjusted by changing the width and spacing of the pentagonal rings, ultimately regulating the resonator's frequency. The duty cycle can also be controlled by varying the area of ​​the load layer relative to the total area, thus achieving different frequencies.

[0050] In addition, the graphical load layer can also be a non-periodic, irregular shape.

[0051] To enable those skilled in the art to better understand the embodiments of the present invention, reference is made to... Figures 12a to 12h The method for forming the resonator according to the embodiments of the present invention is described in detail.

[0052] The structural details in the diagram are described below:

[0053] 10: Substrate, with optional materials including single-crystal silicon, gallium arsenide, sapphire, quartz, silicon carbide, etc.;

[0054] 20: Acoustic mirror, which can be a cavity, or it can be a Bragg reflector layer or other equivalent forms. The embodiments of the present invention are illustrated using the case of a cavity as an example.

[0055] 21: The acoustic mirror filling material can be dielectric materials such as SiO and SiN, or their doped materials;

[0056] 30: Bottom electrode (electrode pin), the material can be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a combination of the above metals or their alloys, etc.;

[0057] 40: Piezoelectric layer, which may be made of materials such as aluminum nitride, zinc oxide, PZT, etc., and contain rare earth element doping materials in a certain atomic ratio of the above materials;

[0058] 50: Top electrode (electrode pin), material or its alloy, etc.;

[0059] 60: The load layer material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or the above metals or their alloys, aluminum nitride, zinc oxide, PZT and other materials, and rare earth element doping materials containing a certain atomic ratio of the above materials;

[0060] 61: Photoresist: It can be negative photoresist or positive photoresist, with negative photoresist being preferred.

[0061] 70: Passivation layer, which can be AlN, SiN, or SiO2;

[0062] 80: Air gap;

[0063] 82: Air gap filling material, which can be dielectric materials such as SiO, SiN and their doped materials.

[0064] like Figure 12a An acoustic mirror filling structure 21 is fabricated on top of the substrate 10. Specifically, a substrate 10 made of single-crystal silicon material is coated with photoresist, and a groove is formed on the top surface of the substrate 10 using photolithography and etching techniques. Then, sacrificial material SiO is deposited, followed by chemical mechanical polishing to form the desired structure. Figure 12a The structure shown.

[0065] like Figure 12b The lower electrode 30 is then fabricated. Specifically, metallic molybdenum is deposited as the electrode material, and then a patterned lower electrode 30 is fabricated using photolithography and etching techniques.

[0066] like Figure 12c A piezoelectric layer 40 is deposited. Specifically, aluminum nitride material is deposited to form the piezoelectric layer 40.

[0067] like Figure 12d The air gap filling material 82 is prepared. Specifically, silicon oxide material is deposited on the piezoelectric layer 40, and then a patterned mask is fabricated on the silicon oxide material. The mask material can be photoresist or a hard mask layer. Then, the area without the mask is etched to remove the silicon oxide material. The mask is then removed to obtain the patterned air gap filling material 82.

[0068] like Figure 12e The top electrode 50 is fabricated. Specifically, metallic molybdenum is deposited as the electrode material, and then a patterned top electrode 50 is fabricated using photolithography and etching techniques.

[0069] like Figure 12f A photoresist with a thickness less than a preset thickness threshold was prepared to obtain the photoresist structure 61 shown in the figure.

[0070] like Figure 12g A load layer material layer, typically Mo, is deposited, and then a lift-off process is performed to remove the photoresist and the load layer material on the photoresist, thus preparing a patterned load layer 60.

[0071] like Figure 12h A passivation layer 70 is prepared, and the acoustic mirror filling structure 21 and the air gap filling material 82 are removed to obtain the acoustic mirror 20 and the air gap 80, thus obtaining the final resonator.

[0072] although Figures 12a to 12hIn the illustrated embodiment, the patterned load layer 60 is disposed below the passivation layer, but this is merely an example and not a limitation. In other embodiments, the load layer 60 can also be flexibly disposed below the bottom electrode 30, below the piezoelectric layer 40, below the top electrode 50, above the passivation layer 70, or inside each film layer.

[0073] The resonator of the embodiments of the present invention can be obtained by any of the resonator forming methods disclosed in the present invention.

[0074] The electronic device according to the embodiments of the present invention includes any of the resonators disclosed in the present invention.

[0075] According to the technical solution of the present invention, the pattern accuracy of the patterned load layer is ensured by controlling the thickness of the photoresist layer, and the processing result has good uniformity and repeatability, which has a beneficial effect on the resonator performance and improves the device yield.

[0076] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for forming a resonator, characterized in that... ,include: An acoustic mirror structure is formed on the substrate; A bottom electrode is formed on the acoustic mirror structure; A piezoelectric layer is formed on the bottom electrode; A top electrode is formed on the piezoelectric layer; It also includes: forming a patterned load layer below the bottom electrode, below the piezoelectric layer, below the top electrode, above the top electrode, or inside each film layer. This step specifically includes: A patterned photoresist layer is formed, wherein the photoresist is a negative photoresist, and the thickness of the photoresist layer is less than a preset thickness threshold. Deposit patterned load layers; Remove the photoresist layer; The preset thickness threshold is 2.8-3.3 micrometers.

2. The method for forming a resonator according to claim 1, characterized in that... , It also includes: forming a passivation layer on the top electrode; The load layer is formed below, above, or inside the passivation layer.

3. The method for forming a resonator according to claim 1, characterized in that... In the step of forming the patterned photoresist layer, the process conditions include: the photoresist viscosity is 10-120 cp.

4. The method for forming a resonator according to claim 3, characterized in that... The process conditions also include: an exposure time of 10-14 seconds and a coating speed of 4000-5000 rpm / s.

5. The method for forming a resonator according to claim 3, characterized in that... The process conditions also include: PEB temperature of 90-120℃; PEB duration of 90-120s.

6. The method for forming a resonator according to any one of claims 1 to 5, characterized in that... The graphical load layer comprises multiple uniformly distributed load islands of the same shape and size.

7. The method for forming a resonator according to claim 6, characterized in that... The shape of the load island is a regular polygon or a circle.

8. The method for forming a resonator according to claim 6, characterized in that... The multiple load islands are arranged in a planar periodic pattern.

9. The method for forming a resonator according to any one of claims 1 to 5, characterized in that... The graphical load layer includes multiple concentric circular rings or multiple concentric polygonal rings as load rings.

10. A method for forming a resonator according to any one of claims 1 to 5, characterized in that... The graphical load layer is an irregular shape.

11. A resonator, characterized in that... It is prepared by the method of forming a resonator according to any one of claims 1 to 10.

12. An electronic device, characterized in that... This includes the resonator as described in claim 11.

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