CN117664040A - Method for nondestructive detection of film thickness based on S11 parameter of surface acoustic wave resonator - Google Patents
Method for nondestructive detection of film thickness based on S11 parameter of surface acoustic wave resonator Download PDFInfo
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- CN117664040A CN117664040A CN202211054551.7A CN202211054551A CN117664040A CN 117664040 A CN117664040 A CN 117664040A CN 202211054551 A CN202211054551 A CN 202211054551A CN 117664040 A CN117664040 A CN 117664040A
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- 238000010897 surface acoustic wave method Methods 0.000 title claims abstract description 40
- 238000000034 method Methods 0.000 title claims abstract description 8
- 238000001514 detection method Methods 0.000 title description 7
- 239000000758 substrate Substances 0.000 claims abstract description 25
- 238000004364 calculation method Methods 0.000 claims abstract description 7
- 238000004088 simulation Methods 0.000 claims abstract description 7
- 239000011159 matrix material Substances 0.000 claims abstract description 5
- 230000008878 coupling Effects 0.000 claims abstract description 4
- 238000010168 coupling process Methods 0.000 claims abstract description 4
- 238000005859 coupling reaction Methods 0.000 claims abstract description 4
- 230000035945 sensitivity Effects 0.000 claims abstract description 3
- 239000000463 material Substances 0.000 abstract description 20
- 238000009659 non-destructive testing Methods 0.000 abstract description 8
- 239000010408 film Substances 0.000 description 18
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 10
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 5
- 235000012239 silicon dioxide Nutrition 0.000 description 5
- 239000000377 silicon dioxide Substances 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 230000005284 excitation Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000002277 temperature effect Effects 0.000 description 1
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- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
The invention belongs to the field of surface acoustic wave nondestructive testing equipment, and particularly relates to a method for measuring the thickness of a film in a film/substrate layered structure based on a surface acoustic wave resonator, which comprises the following steps: a piezoelectric substrate with large electromechanical coupling coefficient and small propagation loss is selected, and a two-dimensional simulation model of a sample wafer to be tested, which comprises a surface acoustic wave interdigital transducer and a film/substrate structure, is built in finite element software; parameters of the piezoelectric substrate and the film and the substrate in the two-dimensional model are determined, wherein the parameters comprise cut angle, young modulus, poisson's ratio, density, elastic matrix and the like; designing structural parameters of an electrode of the surface acoustic wave resonator to obtain an S11 frequency domain curve with high sensitivity; and carrying out frequency domain calculation, extracting an S11 parameter frequency domain curve, and obtaining the resonant frequency of the resonator, so that the curve of the thickness and the resonant frequency of the film to be measured can be fitted. The invention has small volume, convenient carrying, no limitation of material characteristics and wide applicability.
Description
Technical Field
The invention belongs to the field of surface acoustic wave nondestructive testing equipment, and particularly relates to a method for measuring the thickness of a film in a film/substrate layered structure based on a surface acoustic wave resonator.
Background
As ultra-thin film materials are increasingly used in modern integrated circuit research and industry, techniques for non-destructive testing of film properties are also becoming increasingly important. The surface acoustic wave technology is a novel detection means which can be used for detecting the mechanical properties of the film, has the advantages of no damage, accuracy of measurement results, quick and simple detection process, on-line detection and the like, and therefore, the method has good engineering application prospect and profound research significance, and is an important means for nondestructive detection of the properties of the film material. The nondestructive measurement system of the acoustic surface wave resonator adopts the interdigital electrode to excite the acoustic surface wave, has the advantages of low cost and convenient carrying, and is favorable for the equipment of the nondestructive detection technology of the acoustic surface wave. According to the invention, a great amount of simulation calculation research is carried out on a nondestructive testing film thickness model of the surface acoustic wave resonator by utilizing finite element simulation software, the influence of film thickness parameters on the resonant frequency of the surface acoustic wave resonator is researched by changing the thickness of the film to be tested, frequency domain calculation is carried out, an S11 parameter frequency domain curve is extracted, the resonant frequency of the resonator is obtained, and the curve of the thickness of the film to be tested and the resonant frequency is fitted.
Disclosure of Invention
The invention aims to provide a nondestructive testing system capable of realizing miniaturized portable film characteristic measurement, which is designed as a surface acoustic wave resonator, and the surface acoustic wave resonator is modeled by finite element simulation software, and the resonance frequency is obtained through an S11 curve obtained by simulation, so that a fitting curve of the resonance frequency and the material thickness is obtained. The technical scheme of the invention is as follows:
(1) A piezoelectric substrate with large electromechanical coupling coefficient and small propagation loss is selected, and a two-dimensional simulation model of a sample wafer to be tested, which comprises a surface acoustic wave interdigital transducer and a film/substrate structure, is built in finite element software;
(2) Parameters of the piezoelectric substrate and the film and the substrate in the two-dimensional model are determined, wherein the parameters comprise cut angle, young modulus, poisson's ratio, density, elastic matrix and the like;
(3) Designing structural parameters of an electrode of the surface acoustic wave resonator to obtain an S11 frequency domain curve with high sensitivity;
(4) And carrying out frequency domain calculation, extracting an S11 parameter frequency domain curve, and obtaining the resonant frequency of the resonator, so that the curve of the thickness and the resonant frequency of the film to be measured can be fitted.
Drawings
FIG. 1 is a schematic diagram of a nondestructive testing device for a SAW resonator
Fig. 2 finite element model of a surface acoustic wave resonator and a thin film/substrate structure
S11 parameter frequency domain image obtained by frequency domain calculation of finite element simulation software in FIG. 3
FIG. 4 resonant frequency and material thickness curve fitted using Matlab software
Detailed Description
For a better understanding of the present invention, reference is made to the following description, drawings and examples.
(1) FIG. 1 is a schematic diagram of a surface acoustic wave resonator nondestructive testing device. An alternating voltage is applied to the interdigital electrodes through the bus bars, periodic electric field distribution is generated, and elastic deformation is generated on the surface of the dielectric medium due to the inverse piezoelectric effect. The sound waves excited by each pair of the interdigital transducers are mutually overlapped, and according to the interference principle of the waves, the interdigital period lambda is the wavelength lambda of the surface acoustic wave 0 When the integral multiple of the frequency of the external excitation electric signal is equal to the characteristic frequency f of the interdigital electrode, the surface acoustic wave excited by the interdigital electrode is strongest 0 . The reflective grating is a periodically distributed metal grating on the piezoelectric substrate material, which causes the surface impedance discontinuity of the substrate to cause the reflection of the acoustic surface wave, and each reflective grating finger reflects the wave field and interferes with each other. These disturbances cancel each other out, usually over a wide whole band, and the total reflected field is negligible. However, in a certain band range, the phases of the reflected surface acoustic waves are the same, the amplitudes are overlapped, and the stronger reflection characteristic is shown, and the phenomenon is called Bragg reflection. Resonant surface acoustic wave sensor detects resonant frequency f 0 The offset of the interdigital electrode establishes a corresponding relation with external environment parameters, and the characteristic frequency of the interdigital electrode is as follows:
f 0 =v s /λ
in the formula, v s Is the propagation velocity of the surface acoustic wave on the piezoelectric substrate. When the external environment (such as temperature, pressure, etc.) changes, the physical properties of the substrate material or the structural changes of the surface electrode affect the propagation velocity v of the acoustic surface wave s Therefore, the resonance frequency of the surface acoustic wave sensor changes, and the parameters of the external environment can be obtained by detecting the deviation of the frequency;
(2) In FIG. 1, the piezoelectric substrate is made of 128Y-X lithium niobate, the interdigital electrode and the reflecting grating are arranged on a lithium niobate substrate, the electrode material is made of metal aluminum, the electrode thickness h is 600 nm, the width a of the reflecting grating and the interdigital electrode finger strip is 5 μm, the electrode spacing b is 5 μm, the gap L between the reflecting grating and the interdigital electrode is 75 μm, and the interdigital electrode hole is formedThe diameter W is 5 mm, the interdigital electrode pair number is 40, the reflecting grating adopts a short-circuit grating, and the number of the reflecting grating is 50. When the saw resonator is used in practical applications, it is desirable that the resonant frequency of the device does not change with changes in ambient temperature, and the frequency Temperature Coefficient (TCF) of many piezoelectric materials is not zero, so that the lithium niobate material needs to be integrated with the positive TCF film to realize temperature compensation, so as to avoid the temperature effect of the saw resonator. The silicon dioxide guiding layer covers and wraps the metal electrode, and the thickness h of the silicon dioxide guiding layer is 1 1.5 μm;
(3) The finite element model of the surface acoustic wave resonator film/substrate structure is designed based on finite element simulation software, and the simulation adopts a two-dimensional model as shown in fig. 2. As the surface acoustic wave is a surface acoustic wave with the depth of only 1-2 wavelengths, the thickness of the lithium niobate substrate is set to be three times of the wavelength of the surface acoustic wave in simulation, and a Perfect Matching Layer (PML) is added around the model so as to absorb redundant surface acoustic waves. The definition of the piezoelectric material 128 DEG Y-X lithium niobate includes density, elastic matrix, coupling matrix and relative dielectric constant. The metal electrode is made of an aluminum material with built-in software, and has good electrical characteristics. The silicon dioxide guiding layer is made of silicon dioxide material built in software and covers the surface of the electrode. The three parts form the surface acoustic wave resonator, and the material to be tested attached to the silicon substrate is tightly attached to the silicon dioxide guide layer. According to the analysis, a two-dimensional model of the surface acoustic wave resonator measurement system is established;
(4) In the finite element model of the surface acoustic wave resonator film/substrate structure in the step (3), the thickness parameter of the material to be measured is subjected to parameterization scanning and frequency domain calculation, so that frequency domain curves of the S11 parameter of the surface acoustic wave resonator under different thicknesses are obtained, as shown in fig. 3. For the S11 curve of any thickness, when the value of S11 is minimum, the saw resonator is in a resonant state, and the corresponding frequency value is the resonant frequency of the saw resonator, as can be seen from fig. 2, the variation of the thickness of the material to be measured causes the deviation of the S11 parameter, that is, the resonant frequency is changed. When the thickness of the material to be measured is 200 nm, the resonance frequency is 229.8 MHz, and along with the increase of the thickness of the material to be measured, the resonance frequency monotonically decreases, and when the thickness of the material to be measured is 3000 nm, the resonance frequency is 223.1 MHz. Recording the thickness of the material to be measured and the corresponding resonant frequency value, and performing curve fitting on the data by using Matlab software to obtain a theoretical fitting curve and a fitting formula of the resonant frequency of the surface acoustic wave resonator and the thickness of the film, wherein the theoretical fitting curve and the fitting formula are shown in figure 4;
(5) And (3) constructing a nondestructive testing system of the surface acoustic wave resonator to detect the sample wafer, generating a surface acoustic wave in the piezoelectric material through the interdigital electrode, detecting a surface acoustic wave signal at the interdigital electrode through the piezoelectric detector, processing the detected signal through the network analyzer to obtain an S11 curve, namely obtaining the resonance frequency of the surface acoustic wave resonator, and bringing the resonance frequency into a fitting curve shown in fig. 4 to obtain the thickness of the sample wafer.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
The foregoing is merely an example of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. which are within the spirit and principles of the present application are intended to be included within the scope of the claims of the present application.
Claims (1)
1. A method for nondestructively detecting film thickness based on a surface acoustic wave resonator, comprising the steps of:
(1) A piezoelectric substrate with large electromechanical coupling coefficient and small propagation loss is selected, and a two-dimensional simulation model of a sample wafer to be tested, which comprises a surface acoustic wave interdigital transducer and a film/substrate structure, is built in finite element software;
(2) Parameters of the piezoelectric substrate and the film and the substrate in the two-dimensional model are determined, wherein the parameters comprise cut angle, young modulus, poisson's ratio, density, elastic matrix and the like;
(3) Designing structural parameters of an electrode of the surface acoustic wave resonator to obtain an S11 frequency domain curve with high sensitivity;
(4) And carrying out frequency domain calculation, extracting an S11 parameter frequency domain curve, and obtaining the resonant frequency of the resonator, so that the curve of the thickness and the resonant frequency of the film to be measured can be fitted.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211054551.7A CN117664040A (en) | 2022-08-31 | 2022-08-31 | Method for nondestructive detection of film thickness based on S11 parameter of surface acoustic wave resonator |
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| CN202211054551.7A CN117664040A (en) | 2022-08-31 | 2022-08-31 | Method for nondestructive detection of film thickness based on S11 parameter of surface acoustic wave resonator |
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- 2022-08-31 CN CN202211054551.7A patent/CN117664040A/en active Pending
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