SiO2 homogenization method applied to temperature compensation type surface acoustic wave filter
By adjusting the film thickness dispersion after SiO2 coating and combining scanning ion beam etching and chemical mechanical polishing, the problem of SiO2 film thickness uniformity was solved, and the temperature stability and performance of the surface acoustic wave filter were improved.
Patent Information
- Application Number
- CN202511504648.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-21
- Publication Date
- 2026-01-27
AI Technical Summary
In existing technologies, after SiO2 coating, the uniformity of SiO2 film thickness on the wafer surface of surface acoustic wave filter is poor, which affects the filter performance, and the SiO2 planarization effect after chemical mechanical polishing is not good.
After SiO2 coating, the film thickness dispersion is adjusted by scanning ion beam etching, followed by chemical mechanical polishing, and finally homogenization treatment by scanning ion beam etching again to ensure the uniformity of SiO2 film thickness.
It improves the uniformity of SiO2 film thickness, enhances the temperature stability and performance of the filter, and simplifies the process flow.
Smart Images
Figure CN121417841A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of surface acoustic wave filter processing technology, specifically relating to a method for homogenizing SiO2 on the surface of a temperature-compensated surface acoustic wave filter. Background Technology
[0002] Surface acoustic wave (SAW) filters, with their advantages of low insertion loss, high out-of-band rejection, and customizable frequency response, have become key components in mobile communications (such as 4G / 5G RF front-ends), radar systems, the Internet of Things (IoT), and satellite communications. For example, in smartphones, SAW filters are used in RF front-end modules to achieve frequency band isolation and interference immunity.
[0003] The frequency of SAW filters changes with ambient temperature, especially in duplexers or multiplexers, where temperature variations can cause passband shifts, affecting performance metrics such as isolation. Therefore, one of the current research focuses is the design and implementation of temperature compensation techniques. Depositing a layer of SiO2 with a positive temperature coefficient on the surface of an interdigital transducer (IDT) can improve the temperature coefficient of frequency (TCF) of the SAW filter, reduce temperature drift, and the flat SiO2 layer exhibits higher temperature stability and lower stray response. After SiO2 deposition, a height difference is formed between the metal fingers and the metal gaps in the IDT. Currently, the common planarization technique internationally is chemical mechanical polishing (CMP) to eliminate this uneven morphology. However, after CMP, the SiO2 film on the SAW filter wafer surface has poor film thickness uniformity, which affects filter performance and reduces yield. Summary of the Invention
[0004] To solve the above-mentioned technical problems, the present invention provides a method for SiO2 homogenization applied to temperature-compensated surface acoustic wave filters, comprising:
[0005] Measure the SiO2 thickness in the gap area of the metal fingers after the temperature compensation layer is coated;
[0006] Based on the SiO2 film thickness test data after the temperature compensation layer was coated, scanning etching was performed by setting reasonable parameter values using a frequency modulation device to reduce the thickness dispersion of the temperature compensation layer before chemical mechanical polishing.
[0007] The wafer after scanning and etching is subjected to chemical mechanical polishing to planarize the SiO2 on the metal finger area and the gap area.
[0008] The SiO2 thickness in the gap region of the metal fingers was measured again after planarization.
[0009] The thickness test data of SiO2 after planarization was imported into the frequency modulation equipment and appropriate parameters were selected for scanning etching homogenization processing.
[0010] The beneficial effects of this invention are:
[0011] This invention introduces scanning ion beam etching technology before CMP to initially improve the uniformity of SiO2 film thickness and reduce the dispersion effect of CMP on film thickness. Then, scanning ion beam etching is performed again after CMP, which can produce SiO2 with relatively uniform thickness. This solves the problem of film thickness uniformity after SiO2 planarization in temperature-compensated surface acoustic wave filters, and also solves the problem of poor uniformity effect when scanning etching is performed directly after SiO2 planarization. Moreover, the process is relatively simple. Attached Figure Description
[0012] Figure 1 This is a flowchart of SiO2 homogenization applied to a temperature-compensated surface acoustic wave filter according to the present invention;
[0013] Figure 2 This is a cross-sectional schematic diagram of a single chip after the temperature compensation layer has been coated.
[0014] Figure 3 A thickness distribution map generated based on film thickness test results;
[0015] Figure 4 This is a schematic diagram of scanning etching using a frequency modulation device;
[0016] Figure 5 A schematic diagram of SiO2 planarization using chemical mechanical polishing equipment;
[0017] Figure 6 This is a cross-sectional view of a single chip after planarization.
[0018] Figure 7 Map showing the SiO2 thickness distribution after planarization;
[0019] Figure 8 This is a schematic diagram of SiO2 homogenization achieved by scanning etching using a frequency modulation device after planarization.
[0020] Figure 9 This is a schematic diagram of the SiO2 film thickness distribution after CMP only;
[0021] Figure 10 This is a schematic diagram of the SiO2 film thickness distribution after scanning etching following CMP.
[0022] Figure 11 This is a schematic diagram showing the SiO2 film thickness distribution before and after CMP scanning etching.
[0023] In the figure: 1-piezoelectric single crystal, 2-metal part of interdigital transducer, 3-SiO2 part on the gap between metal fingers, 4-SiO2 part on metal fingers. Detailed Implementation
[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0025] like Figure 1 As shown, this invention discloses a method for SiO2 homogenization applied to temperature-compensated surface acoustic wave (SAW) filters, comprising the following steps:
[0026] S101. Complete the SiO2 coating process for the temperature compensation layer on the interdigital transducer.
[0027] like Figure 2 As shown, after the coating is completed, SiO2 will form a height difference between the metal finger area and the finger gap area.
[0028] S102. Measure the SiO2 thickness in the gap between metal fingers on the wafer using a reflection interferometer. The number of test points should be at least 85 points to characterize the thickness distribution of the entire wafer.
[0029] S103. Generate a SiO2 thickness distribution map based on the above test results, such as... Figure 3 As shown;
[0030] S104. Import the thickness distribution map into the frequency modulation equipment and perform scanning etching on the wafer, such as... Figure 4 To reduce film thickness dispersion before chemical mechanical polishing and ensure that the uniformity of SiO2 after scanning etching is less than 1.5%, during the scanning etching process, considering both the scanning etching accuracy and the scanning etching speed, the argon flow rate was selected as 4 sccm, the maximum power was selected as 90W to prevent local overheating and cracking of the wafer, the movement speed was selected as 90mm / sec, and the step size was selected as 1mm to further increase the etching depth.
[0031] S105. Perform chemical mechanical polishing, the process principle is as follows: Figure 5 This process flattens the SiO2 in the metal fingers and inter-metal spaces. To prevent excessive chemical mechanical polishing from reducing film thickness uniformity, the amount of SiO2 removed should not exceed 200 nm.
[0032] like Figure 6 As shown, after chemical mechanical polishing, the SiO2 steps on the original metal finger area and the finger gap area should be flattened.
[0033] S106. Measure the SiO2 thickness in the gap between the metal fingers on the planarized wafer using a reflection interferometer. The number of test points should be at least 85 points to characterize the thickness distribution of the entire wafer.
[0034] S107. Based on the above test results, generate a flattened SiO2 thickness distribution map, such as... Figure 7 As shown;
[0035] S108. The SiO2 planarized thickness distribution map is imported into a frequency modulation device to perform scanning etching on the wafer, completing the final film thickness uniformization. Figure 8 As shown. Similarly, during the scanning etching process, the argon flow rate was selected as 4 sccm, the maximum scanning etching power was set to 90W, the moving speed during scanning etching was selected as 90 mm / sec, and the step size was 1 mm. After scanning etching, the SiO2 uniformity can reach 2.0%.
[0036] In this embodiment, the effects of the present invention are experimentally verified:
[0037] Existing technology: Chemical mechanical polishing (CMP) is performed after the temperature compensation layer is deposited to smooth out the SiO2 protrusions on the metal fingers. While CMP can eliminate the unevenness of SiO2 in the metal fingers and inter-metal gap areas on a single chip, it reduces the uniformity of SiO2 thickness across the entire wafer. Figure 9 As shown, the thickness dispersion range is up to 100 nm, and the uniformity is 3.6%.
[0038] This invention addresses the issue of uniform SiO2 thickness across a wafer by introducing frequency-modulated etching (ion beam scanning etching). This approach utilizes Ar ion beams for physical scanning etching, which offers advantages such as strong anisotropy, high precision, and high surface cleanliness. However, physical scanning etching has limited etching capacity; for wafers with significant SiO2 thickness dispersion, multiple scanning etching processes are required, and the etching effect is often poor. Following CMP (Chemical Metallurgy) with Ar ion scanning etching yields the following results: Figure 10 As shown, the improvement effect is very limited, the dispersion range is still as high as 90nm, and the uniformity is 3.3%.
[0039] Before CMP (i.e., after SiO2 coating), an Ar ion beam scanning etching is performed. Because the SiO2 coating exhibits relatively low thickness dispersion and a fairly uniform thickness gradient, this thickness distribution is beneficial for Ar ion beam physical scanning etching. This process first improves the wafer thickness uniformity to a high level before CMP. After this treatment, the thickness dispersion of the wafer after CMP will also be reduced. A subsequent Ar ion beam scanning etching can then significantly improve the SiO2 thickness uniformity. Figure 11 As shown, the SiO2 thickness uniformity can reach 1.9%.
[0040] The method for homogenizing the SiO2 in the temperature compensation layer of a temperature-compensated surface acoustic wave (SAW) filter disclosed in this invention achieves better SiO2 uniformity on a single wafer compared to existing technologies that only use chemical mechanical polishing. Furthermore, it compensates for the poor performance of scanning etching performed only after chemical mechanical polishing.
[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for SiO2 homogenization applied to temperature-compensated surface acoustic wave filters, characterized in that, include: Measure the SiO2 thickness in the gap area of the metal fingers after the temperature compensation layer is coated; Based on the SiO2 film thickness test data after the temperature compensation layer was coated, the parameter values of the frequency modulation equipment were scanned and etched to reduce the thickness dispersion of the temperature compensation layer before chemical mechanical polishing. The wafer after scanning and etching is subjected to chemical mechanical polishing to planarize the SiO2 on the metal finger area and the gap area. The SiO2 thickness in the gap region of the metal fingers was measured again after planarization. The thickness test data of SiO2 after planarization is imported into the frequency modulation equipment for scanning etching homogenization processing.
2. A method for SiO2 homogenization applied to a temperature-compensated surface acoustic wave filter according to claim 1, characterized in that, When measuring the thickness of the temperature compensation layer SiO2, the number of test points should be at least 85 to characterize the overall SiO2 film thickness distribution on the wafer surface.
3. A method for SiO2 homogenization applied to a temperature-compensated surface acoustic wave filter according to claim 1, characterized in that, After the temperature compensation layer SiO2 is deposited, scanning etching should be performed before chemical mechanical polishing. After scanning etching, the uniformity of SiO2 film thickness is less than 1.5%.
4. A method for SiO2 homogenization applied to a temperature-compensated surface acoustic wave filter according to claim 1, characterized in that, During chemical mechanical polishing, the amount of SiO2 removed should not exceed 200 nm.
5. A method for SiO2 homogenization applied to a temperature-compensated surface acoustic wave filter according to claim 1, characterized in that, The parameters of the frequency modulation equipment are scanned and etched, including: The argon flow rate was set to 4 sccm, the maximum scanning etching power was set to 90 W, the moving speed during scanning etching was set to 90 mm / sec, and the step size was less than 1 mm.