Surface acoustic wave resonator mass load preparation process and semiconductor structure
By using a new photoresist layer transfer process and thin film deposition and peeling method when preparing surface acoustic wave resonators, the problems of incising accuracy and alignment offset between the interdigital electrode and the mass loading layer are solved, which improves product consistency and quality and reduces process difficulty.
Patent Information
- Application Number
- CN202411615806.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-13
- Publication Date
- 2025-02-28
AI Technical Summary
In the preparation of temperature-compensated surface acoustic filter (TC-SAW), the interlacing accuracy between the interlaced electrode and the mass load layer is high, and due to factors such as wafer warping, the alignment deviation between the interlaced electrode and the mass load layer is increased, which increases process difficulty and clutter problems.
Using a new mass load preparation process for surface acoustic wave resonators, the IDT and mass load patterns are transferred to the wafer by forming the first and second photoresist layers on the wafer, respectively, and the IDT and mass load material film are deposited and peeled off without peeling the first photoresist to reduce the incision offset.
Reduced requirements for intercalation accuracy, improved product consistency and quality, reduced requirements for lithography machine capabilities and wafer flatness, and avoided the need to use OPC technology to correct graphics deviations.
Smart Images
Figure CN119543860A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of radio frequency filters, and in particular relates to a surface acoustic wave resonator mass load preparation process and a semiconductor structure. Background Art
[0002] The main function of a radio frequency (RF) filter is to attenuate signals in certain unwanted frequency bands while having minimal impact on signals in the desired frequency bands. RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in the RF front end of cellular base stations, mobile phones and computing devices, satellite transceivers and ground base stations, IoT (Internet of Things) devices, laptops and tablets, fixed-point radio links, and other communication systems. RF filters are also used in radars, as well as electronic and information warfare systems.
[0003] High-performance RF filters used in current communication systems usually include acoustic wave resonators, including surface acoustic wave resonators (SAW), bulk acoustic wave resonators (BAW), film bulk acoustic wave resonators (FBAR), and transversely excited film bulk acoustic wave resonators (XBAR), etc. Among them, in order to improve the temperature characteristics of the surface acoustic wave resonator (SAW), a temperature compensated SAW (TC-SAW) is formed by covering its IDT (interdigital transducer). Due to the presence of the temperature compensation layer, the temperature characteristics of TC-SAW are significantly improved compared to SAW.
[0004] Temperature compensated surface acoustic wave filters usually require mass loading on the interdigital fingers to suppress the noise due to the high noise. This mass loading layer is also called piston. The traditional process for preparing interdigital transducers (IDTs) and pistons is as follows: IDT lithography-IDT coating-IDT stripping; piston lithography-piston coating-piston stripping. Since the CD (line width) of IDT and piston is small, the alignment offset between the two layers becomes non-negligible. Coupled with the warping of the wafer itself, the offset of the two layers is further aggravated, such as Figure 1 , which is a partial view of a TC-SAW prepared by the existing process under an optical microscope, in which the strip 1 is the interdigital electrode of the IDT, and the oval 2 is the piston.
[0005] Since the interdigital electrodes of SAW devices are relatively narrow (micrometer to submicrometer level), and as the frequency increases, the interdigital electrodes will become narrower. The preparation of piston structures on interdigital electrodes requires very high overlay accuracy, which puts higher requirements on the capabilities of photolithography machines, photolithography processes, wafer flatness, etc. At the same time, since the piston line width is narrower than the line width of the interdigital electrodes, the shape of the graphics is deviated, and optical proximity correction (OPC) technology needs to be added to correct the deviation as much as possible, which further increases the difficulty of optimizing the photolithography process. Summary of the invention
[0006] In order to solve the above problems, the present invention provides a surface acoustic wave resonator mass loading preparation process and semiconductor structure. The use of this process greatly reduces the requirements for overlay accuracy, can better control the consistency of products and improve product quality.
[0007] The technical solution adopted by the present invention is:
[0008] The present application discloses a surface acoustic wave resonator mass loading preparation process, comprising:
[0009] Prepare a wafer; use a photolithography process to form a first photoresist layer on the wafer, the first photoresist layer is used to transfer the IDT pattern on the first mask to the wafer; deposit a layer of IDT material film according to the design thickness requirement on the wafer formed with the first photoresist layer; form a second photoresist layer on the wafer after IDT coating, the second photoresist layer is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer; deposit a layer of mass load material film according to the design thickness requirement on the wafer formed with the second photoresist layer; finally, peel off the photoresist on the wafer, so that the IDT material film and / or the mass load material film covering the photoresist are peeled off together, and the IDT material film and the mass load material film not covering the photoresist are retained.
[0010] As an optional technical solution, the wafer is made of lithium niobate, lithium tantalate, Si, SiC, GaN, Al2O3 or diamond semiconductor material.
[0011] As an optional technical solution, the IDT material layer is a combination of two or more materials selected from the group consisting of metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW.
[0012] As an optional technical solution, the mass load material layer is a combination of two or more materials selected from the group consisting of metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW.
[0013] As an optional technical solution, the first photoresist layer has a first process window, and the second photoresist layer has a second process window, and the width of the second process window is greater than the width of the first process window by 70nm-1000nm.
[0014] As an optional technical solution, a lift-off process is used to strip the photoresist on the wafer.
[0015] The present application also discloses a semiconductor structure, which is applied to the mass load preparation process of the surface acoustic wave resonator as mentioned above, and the semiconductor structure includes: a wafer; a first photoresist layer formed on the wafer, and the first photoresist layer is used to transfer the IDT pattern on the first mask to the wafer; an IDT material film formed on the wafer and the first photoresist layer; a second photoresist layer formed on the IDT material film, and the second photoresist layer is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer; and a mass load material film formed on the second photoresist layer and the IDT material film.
[0016] As an optional technical solution, the first photoresist layer has a first process window, and the second photoresist layer has a second process window, and the width of the second process window is greater than the width of the first process window by 70nm-1000nm.
[0017] The beneficial effects of the present invention are as follows: the use of the preparation process of the present application greatly reduces the requirements for overlay accuracy, so the requirements for lithography machine capabilities, lithography processes, wafer flatness, etc. are also lower than those of traditional processes. At the same time, the CD of the piston structure of the preparation process of the present application on the photolithography plate is wider than the interdigital electrode, and compared with the traditional piston structure, it does not need to use OPC technology to correct graphic deviations. The use of the process of the present application can better control the consistency of products and improve product quality. In short, for the preparation process of the present application, the process difficulty is smaller, and the quality stability and consistency of the prepared products are better. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is a partial view of the TC-SAW prepared using the existing process under an optical microscope.
[0019] Figure 2 Schematic diagram of the lift-off process.
[0020] Figure 3-Figure 7 These are the semiconductor structures formed during the preparation process of this embodiment.
[0021] Figure 8 This is a partial view of the TC-SAW prepared by the process of this embodiment under an optical microscope.
[0022] Fig. 9 FIG. 4 is a schematic flow chart of a process for preparing a surface acoustic wave resonator mass load according to the present embodiment. DETAILED DESCRIPTION
[0023] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.
[0024] In order to better understand the present embodiment, the lift-off process involved in the present embodiment is first briefly introduced.
[0025] In the field of semiconductor preparation, the lift-off process is one of the commonly used pattern transfer process technologies. Pattern transfer refers to the process of transferring the circuit diagram from the mask to the wafer.
[0026] like Figure 2 As shown, a photoresist pattern is formed on the wafer using a photoresist ( Figure 2 Figure a and Figure b), then deposit a thin film (such as aluminum) to cover the photoresist and substrate ( Figure 2 c), the thickness of this film must be thinner than the photoresist; then, as the photoresist will dissolve in the appropriate etching solution, the part of the film covering the photoresist (pseudo-film) will be selectively stripped and removed ( Figure 2 (d)
[0027] For TC-SAW, the existing preparation process is to use the lift-off process to first deposit the IDT film on the wafer and peel off the pseudo-IDT film, and then use the lift-off process to deposit the piston film on the IDT and peel off the pseudo-piston film. There is an overlay offset between the two times. The overall inventive concept of the present invention is: after depositing the IDT film, the pseudo-IDT film is not peeled off, but the piston film is directly deposited on the IDT film again using the lift-off process, and finally peeled off to remove the pseudo-IDT film and the pseudo-piston film together. Based on the above description, the embodiments of the present application are described in detail below.
[0028] Example
[0029] This embodiment discloses a surface acoustic wave resonator mass loading preparation process, such as Fig. 9 As shown, including:
[0030] S1. Prepare a wafer, wherein the wafer can be made of lithium niobate, lithium tantalate, Si, SiC, GaN, Al2O3 or diamond semiconductor materials.
[0031] S2, forming a first photoresist layer 4 on the wafer 3 by using a photolithography process, such as Figure 3 .
[0032] Specifically, the wafer 3 is placed on a vacuum-adsorbed rotating disk, and the photoresist is dropped on the center of the wafer 3. Then the wafer 3 is quickly accelerated to the set rotation speed and maintained for a period of time. It should be noted that the photoresist should be evenly coated. After spin coating, the wafer is pre-baked. Then, using an optical graphic exposure system, the wafer 3 is aligned with the first mask and the photoresist is exposed using ultraviolet light. The exposed photoresist (positive photoresist) will be dissolved in the developer (the opposite is true for negative photoresist). After development, the wafer is post-baked. Finally, the image is obtained as shown below. Figure 3 The semiconductor structure shown in FIG. 1 is then transferred from the IDT pattern on the first mask to the wafer 3 using the first photoresist layer 4 .
[0033] S3, depositing a thin film 5 of IDT material on the wafer 3 with the first photoresist layer 4 according to the design thickness requirement, such as Figure 4 The IDT material layer is a combination of two or more materials selected from the group consisting of metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW. Specifically, the deposition of the IDT material film 5 can be carried out by a physical vapor deposition process such as evaporation, electron beam evaporation, plasma spraying, and sputtering.
[0034] In the existing TC-SAW preparation process, after this step, the photoresist will be stripped to remove the pseudo film. This embodiment has improved it. After step S3 is completed, the photoresist will not be stripped, but step S4 will be directly performed to overcome the overlay offset problem twice before and after. Due to the overlay offset problem, the piston CD of the traditional process route is usually smaller than the IDT CD, otherwise it will deviate from the IDT. The technical solution proposed in this patent can allow the piston CD (i.e., the second process window D2 in this embodiment) to be larger than the IDT CD (i.e., the first process window D1 in this embodiment), and preferably D2-D1 is larger than the overlay offset overlay (i.e., piston CD>IDT CD+overlay). This is because the piston film layer that exceeds the IDT part will be stripped off in the final stripping process due to the presence of the IDT layer photoresist.
[0035] S4, forming a second photoresist layer 6 on the wafer 3 after the IDT coating is completed, such as Figure 5 The second photoresist layer 6 is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer. The formation of the second photoresist layer 6 can refer to the formation process of the first photoresist layer 4 in step S2, and the mask used for exposure is changed to the second mask. The other processes are roughly the same and will not be described in detail here.
[0036] S5, depositing a thin film 7 of mass-loaded material on the wafer 6 formed with the second photoresist layer 6 according to the design thickness requirement, such as Figure 6 ; Wherein, the mass load material layer is a combination of two or more materials selected from metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW. Specifically, the deposition of the mass load material film 7 can be carried out by physical vapor deposition processes such as evaporation, electron beam evaporation, plasma spraying, and sputtering.
[0037] S6, finally peeling off the photoresist (4, 6) on the wafer, so that the IDT material film 5 and / or the mass load material film 7 covering the photoresist (4, 6) are peeled off together, and the IDT material film 5 and the mass load material film 7 not covering the photoresist are retained, and finally the following is obtained: Figure 7 The semiconductor structure shown in FIG. 1 is a semiconductor structure in which a lift-off process is used to remove the photoresist on the wafer. Figure 7 A partial view of the semiconductor structure shown under an optical microscope is shown in Figure 8 ,and Figure 1 Compared with the offset in Figure 8 There is almost no offset between the mass load film 7 and the IDT material film 5.
[0038] As an optional implementation, Figure 5 and Figure 6 As shown, the first photoresist layer has a first process window, the second photoresist layer has a second process window, and the width of the second process window D2 is greater than the width of the first process window D1 by 70nm-1000nm.
[0039] This embodiment also discloses a semiconductor structure, which is applied to the mass loading preparation process of the surface acoustic wave resonator as described above, such as Figure 6As shown, the semiconductor structure includes: a wafer 3; a first photoresist layer 4 formed on the wafer 3, the first photoresist layer 4 is used to transfer the IDT pattern on the first mask to the wafer 3; an IDT material film 5 formed on the wafer 3 and the first photoresist layer 4; a second photoresist layer 6 formed on the IDT material film 5, the second photoresist layer 6 is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer; a mass load material film 7 formed on the second photoresist layer 6 and the IDT material film 5.
[0040] As an optional implementation, the first photoresist layer 4 has a first process window, the second photoresist layer 6 has a second process window, and a width D2 of the second process window is greater than a width D1 of the first process window by about 70 nm-1000 nm.
[0041] The above description is only a specific implementation mode of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. All technical solutions that fall within the scope defined by the claims of the present invention fall within the protection scope of the present invention.
Claims
1. A surface acoustic wave resonator mass loading preparation process, characterized in that: include: Prepare the wafer; Forming a first photoresist layer on the wafer by using a photolithography process, wherein the first photoresist layer is used to transfer the IDT pattern on the first mask to the wafer; Depositing a thin film of IDT material on the wafer having the first photoresist layer according to the designed thickness requirement; forming a second photoresist layer on the wafer after the IDT coating is completed, wherein the second photoresist layer is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer; Depositing a thin film of mass-loaded material on the wafer having the second photoresist layer formed thereon according to the designed thickness requirement; Finally, the photoresist on the wafer is stripped off, so that the IDT material film and / or the mass load material film covering the photoresist are stripped off together, and the IDT material film and the mass load material film not covering the photoresist are retained.
2. The surface acoustic wave resonator mass loading preparation process according to claim 1, characterized in that: The wafer is made of lithium niobate, lithium tantalate, Si, SiC, GaN, Al2O3 or diamond semiconductor material.
3. The surface acoustic wave resonator mass loading preparation process according to claim 1, characterized in that: The IDT material layer is a combination of two or more materials selected from the group consisting of metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW.
4. The surface acoustic wave resonator mass loading preparation process according to claim 1, characterized in that: The mass load material layer is a combination of two or more materials selected from the group consisting of metals Ti, Al, Cu, Cr, Ag, Mo, W, Pt, AlCu alloy, and TiW.
5. The surface acoustic wave resonator mass loading preparation process according to claim 1, characterized in that: The first photoresist layer has a first process window, and the second photoresist layer has a second process window. The width of the second process window is greater than the width of the first process window by 70nm-1000nm.
6. The surface acoustic wave resonator mass loading preparation process according to claim 1, characterized in that: When stripping the photoresist on the wafer, a lift-off process is used.
7. A semiconductor structure, applied to the mass loading preparation process of a surface acoustic wave resonator as claimed in any one of claims 1 to 6, wherein: The semiconductor structure comprises: Wafer; A first photoresist layer is formed on the wafer, wherein the first photoresist layer is used to transfer the IDT pattern on the first mask to the wafer; An IDT material film formed on the wafer and the first photoresist layer; A second photoresist layer formed on the IDT material film, wherein the second photoresist layer is used to transfer the mass load pattern on the second mask to the IDT pattern formed on the wafer; A mass loading material film is formed on the second photoresist layer and the IDT material film.
8. The semiconductor structure according to claim 7, characterized in that: The first photoresist layer has a first process window, and the second photoresist layer has a second process window. The width of the second process window is greater than the width of the first process window by 70nm-1000nm.