A cross-scale film stress testing system and testing method

Abstract

The present invention designs a cross-scale thin film stress testing system and testing method. First, the sample film is placed on the sample plate. The light reflected by the uneven film is transmitted by a helium-neon laser. After being received and processed by the line CCD, the light signal is converted into an amplified electrical signal. The computer calculates the warpage and the macroscopic stress of the film is obtained after formula derivation, and the area that needs further measurement is determined. Then, without moving the sample, the local microscopic stress is measured using the principle of X-ray diffraction. The X-rays are reflected by the crystal plane to obtain several beams of diffraction lines. The deformation between the crystal planes is obtained using the X-ray diffraction conditions, and the stress on the microscopic crystal is calculated. The technical method of the present invention can greatly save time and materials for monitoring the macroscopic warpage condition and the microscopic grain arrangement state of the thin film material, and the stress state of the thin film material can be detected based on the measurement results. It has the advantages of simple and fast operation, time and cost saving, and a wide range of applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of photomechanical thin film stress measurement, and in particular relates to a cross-scale thin film stress testing system and testing method. Background Art

[0002] Diversified thin films are widely used in scientific and technological fields such as airborne, satellite, and aerospace. Their combination with microcircuits is an important branch in the thin film field, known as thin film circuits. This is a multi-layer interconnected circuit structure in which chips are made using vacuum coating, sputtering, electroplating and other film-forming processes, as well as dry and wet etching and other molding technologies. Due to the high interconnection density and line precision, thin film technology can achieve small hole metallization, the manufacture of passive circuit integrated components, and the manufacture of multi-layer circuits. Due to the outstanding characteristics of the components produced, such as a wide parameter range, high precision, high integration, and small size, it is a very competitive microwave circuit module in the high-precision field. The macroscopic failure process of thin films and the nanoscale mechanical properties are related to the material life and microstructural state, so quantitative detection of the stress state of thin film materials is of great significance.

[0003] Curvature methods for measuring film stress include the cantilever beam method, Newton ring method, and interferometer phase-shift stress measurement. The cantilever beam method measures the bending deformation of the substrate to which the film is attached to obtain macroscopic stress in the film. The Newton ring method utilizes the phenomenon of interference fringes between the curved surface of the film after coating and the reference plane of the substrate. Substituting the Newton ring spacing and the number of fringes into the Newton ring stress formula, the stress value can be calculated. The interferometer phase-shift stress measurement method uses a CCD to convert the interference pattern signal between the film curved surface and the reference plane into a digital signal to obtain the film's radius of curvature and its stress state.

[0004] X-ray diffraction (XRD) is the most commonly used method for measuring stress in nanoscale thin films. X-ray diffraction is used to measure stress or strain. X-ray diffraction measures the distortion of the crystal lattice under stress, and the Bragg diffraction formula is used to determine the change in the interplanar spacing of the microcrystals in the film structure, giving the film's microscopic stress value.

[0005] Currently, commonly used thin film stress testing methods can only measure a single scale range, either macroscopic or microscopic. Furthermore, adding microscopic stress measurement points after macroscopic measurements is prone to positioning errors. There is a lack of an instrument that can effectively save time and costs while measuring multiple parameters simultaneously. The cross-scale thin film stress testing system was invented to address these issues. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a cross-scale thin film stress testing system and testing method, which can eliminate the positioning step during cross-scale measurement, perform rapid in-situ measurement, have high positioning accuracy, and improve measurement efficiency.

[0007] The technical solution adopted by the present invention to solve its technical problems is: first, a cross-scale thin film stress testing system is provided, which includes a macro measurement module and a micro measurement module, which are stress measurement path modules for macro and micro measurement of thin film strain respectively. The components of the macro measurement module and the micro measurement module are spatially staggered, and the detection optical paths of each other do not affect each other, and are used for simultaneous positioning and continuous measurement of the stress state of a specified area of ​​the pattern across scales.

[0008] According to the above technical solution, in the macro measurement module, the laser emission and etalon are arranged sequentially in the direction of the incident light path, and the linear array CCD, polarizer, and receiver are arranged sequentially in the reflected light path to ensure that the laser light can be received. An external computer calculates the maximum macrostress area (5MPa-50GPa) and the average stress value for a localized area of ​​the sample (80mm*80mm operating table) of 0.3-20m. The laser light emitted by the laser is processed by the etalon-linear array CCD-polarizer into several parallel beams. The reflected light is then received, and the light intensity is reduced due to polarization to prevent photoelectric oversaturation.

[0009] According to the above technical solution, in the micro-measurement module, the emitter, primary Soller slit, automatic divergence slit, and ray shield are arranged in sequence along the incident light path, allowing light to reach the sample box extending from the central axis of the goniometer. A sequence of slit, secondary Soller slit, anti-scatter slit, sealed box, monochromator, detector slit, and detector is arranged along the diffraction light path between the sample and the detector, allowing the diffracted light to be received. The emitter emits incident X-rays, which are then dispersed through the primary Soller slit, automatic divergence slit, and ray shield, limiting their height and width, before reaching the sample box extending from the central axis of the goniometer. Diffracted rays from the sample to the detector pass through the slit, secondary Soller slit, anti-scatter slit, sealed box, monochromator, detector slit, and detector exit, where they are aligned with the Kα wavelength and limited in divergence before being received. The received diffraction signals are recorded in an external computer, generating a diffraction pattern, which provides data on the position, intensity, and line shape of the diffracted rays and is used to calculate the film's microstress.

[0010] According to the above technical solution, the laser is a helium-neon laser.

[0011] According to the above technical solution, the angular velocity ratio between the detector and the sample table is 2:1.

[0012] The present invention also provides a cross-scale film stress testing method, which includes the following steps: step 1, testing the stress of the film at a macro scale, placing the sample film on a sample plate, using light interference, and the reflected light of the helium-neon laser passing through the uneven film, and then converting the light signal into an amplified electrical signal; step 2, calculating the warpage and the macroscopic stress of the film by computer, and determining the area that needs further measurement; step 3, testing the stress of the film at a micro scale, continuing to use X-ray diffraction to measure the local microscopic stress without moving the sample, and obtaining several beams of diffraction lines by X-ray reflection after the crystal plane; step 4, using X-ray diffraction conditions to obtain the deformation between crystal planes, and calculating the stress on the microscopic crystal.

[0013] According to the above technical solution, in step 1, the optical signal is converted into an amplified electrical signal and processed specifically by the line CCD.

[0014] According to the above technical solution, in step 2, the macroscopic stress of the film is obtained as follows:

[0015]

[0016] Where σ f ——Residual stress of the measured film, Ms——Young's modulus of the matrix, M f ——Young's modulus of the film, h s ——matrix thickness, h f ——film thickness, ρ1——radius of curvature of the sample before film deposition, ρ2——radius of curvature of the sample after film deposition.

[0017] According to the above technical solution, in step 4, the microscopic crystal is subjected to stress as follows:

[0018]

[0019] ——the angle between the vertical plane and the normal direction of the incident and outgoing rays, E——Young's modulus of the sample, v——Poisson's ratio of the sample, --different The distance between the crystal planes at the time of value, d0—— is the interplanar spacing of the crystal plane.

[0020] The present invention has the following beneficial effects: The technical method of the present invention significantly reduces the time and materials required to monitor the macroscopic warpage and microscopic grain arrangement of thin film materials, and enables the detection of the stress state of the thin film materials based on the measurement results. The thin film stress testing system of the present invention is simple and quick to operate, saves time and costs, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0022] Figure 1 1 is a schematic diagram of the overall structure of a thin film stress testing system according to an embodiment of the present invention;

[0023] Figure 2 This is the principle of measuring the stress of a flat film using the macro-scale curvature method in the implementation of the present invention;

[0024] Figure 3 This is the principle of measuring stress in curved films using the macroscale curvature method in the implementation of the present invention;

[0025] Figure 4 It is a schematic diagram of the interplanar spacing of the same family of crystals in different orientations in a micro-scale X-ray diffractometer in the embodiment of the present invention;

[0026] Figure 5 It is the principle of microscopic scale X-ray diffractometer in the implementation of the present invention;

[0027] Figure 6 This is a test flow chart of a thin film stress testing method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] In the embodiment of the present invention, Figure 1 As shown, it includes an X-ray source 1, a primary Soller slit 2, an automatic divergence slit 3, an anti-scattered light barrier 4, a sample box 5, a receiving slit 7, a secondary Soller slit 8, an anti-scattered slit sealing box 9, a monochromator 10, a detector slit 11, an X-ray detector 12, a He-Ne laser 13, an etalon 14, a polarizer 15, a linear array CCD 16, and a goniometer 17.

[0030] The incident light emitted by the helium-neon laser 13 is divided into several parallel light beams by the etalon 14, which are then emitted onto the surface of the sample, and the linear CCD 16 receives the reflected light. The function of the CCD image sensor is to convert the optical signal into an analog current signal, and then amplify and convert the current signal into analog-to-digital. The optical path image undergoes acquisition, storage, transmission, processing and reproduction, and finally the computer displays the light intensity image of the light spot. When stress causes the sample to be slightly concave or slightly convex, the position image of the light spot appears close or separated. The light intensity is weakened by the polarizer 15, which can only pass light with the same vibration direction as the polarizer, and the CCD will not be photoelectrically oversaturated. After computer calculation, the local macroscopic stress area of ​​the sample with large stress and the average stress value can be obtained for further microscopic research.

[0031] X-rays are emitted by emitter 1. A primary Soller slit 2 in the incident light path limits X-ray divergence in the height direction, while an automatic divergence slit 3 limits divergence in the width direction. Anti-scatter beams 4 and 11 function identically. The central axis of the goniometer 17 extends outward from the sample stage 5 and can rotate about its central axis. The necessary instruments for the optical path are arranged along the circumference of the goniometer, and the angular velocity ratio between the detector and the sample stage is 2:1 to satisfy the Bragg formula. To address the divergence of diffracted rays, a receiving slit 7, a secondary Soller slit 8, and a receiving anti-scatter slit sealing box 9 are provided in the optical path from the sample to the detector. This ensures that only diffracted rays focused toward the detector are received, while stray rays are blocked. A graphite bent crystal monochromator is aligned with the Kα diffracted rays, eliminating Kβ radiation and background.

[0032] The rotating sample stage simultaneously records the diffraction signals from each crystal plane received by the detector into the data processing system, generating a diffraction pattern and obtaining precise data such as the position, intensity, and line shape of the diffraction lines. The microscopic stress of the film can then be calculated. This completes the cross-scale stress measurement of the film.

[0033] In the film stress testing method according to the embodiment of the present invention, the steps are as follows: Figure 6 After placing the sample, turn on the laser. Figure 2 Diagram of the optical path reflected from the flattened film 21: He-Ne laser light emitted by He-Ne laser 13 is altered in angle by a rotatable oscillating mirror 24, and a lens converts the incident light 26 into a linear scanning beam that travels across the wafer. The reflected light rays are incident on each other through the wafer, with the same difference in reflection angle. Therefore, all rays are focused on the same point on the planar photodiode. Figure 2 This is a diagram of light reflected from the curved film 22. When the film sample presents a slightly concave or convex shape under stress, the reflected light enters the receiver at different angles and hits the photodiode at different points, forming light spots that are close to or separated from each other. Figure 3 This is the principle of measuring stress of curved films using the macro-scale curvature method in the implementation of the present invention.

[0034] Applicable to Figure 1 It can be seen that when sample 6 has a small bending deformation and the incident angle is small, the substrate curvature k can be obtained by the formula:

[0035]

[0036] Where L is the distance from the sample center to the CCD surface;

[0037] D0 - the distance between the centers of adjacent incident beams;

[0038] D——The distance between the centers of the corresponding adjacent reflected beams. The reflection angle is approximately equal to the incident angle α;

[0039] The stress can then be obtained using the Brenner-Senderoff modified Stoney's formula.

[0040]

[0041] Where σ f ——Residual stress of the measured film, Ms——Young's modulus of the substrate, Mf——Young's modulus of the film, hs——substrate thickness, hf——film thickness, ρ1——radius of curvature of the sample before deposition of the film, ρ2——radius of curvature of the sample after deposition of the film.

[0042] After obtaining the macro-scale average stress of the film, turn off the laser and turn on the X-ray diffractometer. Figure 4 In the figure, A is a displaced crystal, B is a normal crystal, a is the optical path difference of the incident light, b is the optical path difference of the outgoing light, and the interplanar spacing is represented by d. Figure 4 The figure illustrates the interplanar spacing of crystals of the same family in different orientations. Even if the growth environment of the same crystal changes the morphology, the angle between the crystal planes remains unchanged. Tensile stress perpendicular to a crystal plane increases the interplanar spacing in that direction, while compressive stress decreases it. The greater the stress, the more pronounced the difference in interplanar spacing, and consequently, the greater the difference in diffraction angle.

[0043] The mechanism of X-ray diffraction relies on certain specific conditions: due to the periodicity of the crystal structure, the crystal can be viewed as a stack of parallel atomic planes with equal spacing between the interplanar planes. Because X-rays are highly penetrating, they illuminate all atomic planes of the crystal. Furthermore, because the distance between the test equipment and the sample is many orders of magnitude greater than the interplanar spacing, both the incident and reflected rays are approximately parallel. Unlike mirror reflection, which can occur at any angle, X-rays are selectively reflected from crystal planes, governed by Bragg's law. Figure 5 The Bragg formula is shown as:

[0044] 2d sinθ=nλ

[0045] d is the distance between the diffraction planes, also known as the interplanar spacing; θ is the angle between the incident X-ray and the corresponding crystal plane; λ is the wavelength of the X-ray; and n is the diffraction order. Diffraction occurs only when the optical path difference between two adjacent crystal planes is n times the X-ray wavelength. When incident parallel light strikes parallel atomic planes in a crystal, and the optical path difference of the reflected light satisfies the aforementioned geometric relationship, and the angle of incidence is equal to the scattering angle, the diffraction intensity of the light is enhanced, which is called interference.

[0046] The diffraction of X-rays in a crystal is, in principle, the interference of coherently scattered waves from the crystal planes. Since the diffraction direction is equal to the reflection of the incident ray by the crystal plane, Bragg's law, representing the law of reflection, can be used to explain diffraction. The obtained crystal plane distance is applied to the following formula to obtain the microscopic stress of the pattern.

[0047]

[0048] ——the angle between the vertical plane and the normal direction of the incident and outgoing rays, E——Young's modulus of the sample, v——Poisson's ratio of the sample, --different The distance between the crystal planes at the time of value, d0—— is the interplanar spacing of the crystal plane.

[0049] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A cross-scale film stress testing method, characterized in that: The method includes the following steps: Step 1, testing the stress of the film at a macro scale, placing the sample film on a sample plate, using light interference, the helium-neon laser passes through the reflected light of the uneven film, and then converts the optical signal into an amplified electrical signal; in the macro measurement module, the laser emission and the standard tool are arranged in sequence in the direction of the incident light path, and the linear array CCD, polarizer, and receiver are arranged in sequence in the reflected light path so that the laser can be received; Step 2, calculating the warpage and the macro stress of the film by computer, and determining the area that needs further measurement; the macro stress of the film is obtained specifically as follows: Where, σf is the residual stress of the film, Ms is the Young's modulus of the matrix, M f ——Young's modulus of the film, h s ——matrix thickness, h f ——film thickness, ρ1——radius of curvature of the sample before film deposition, ρ2——radius of curvature of the sample after film deposition; Step 3: Testing film stress at the microscale. X-ray diffraction is used to measure local microstress without moving the sample. X-rays are reflected from the crystal plane to produce several diffraction rays. In the micro-measurement module, the emitter, primary Soller slit, automatic divergence slit, and ray shield are sequentially arranged on the incident light path, allowing the light to reach the sample box extending from the center axis of the goniometer. Between the sample and the detector, the diffraction light path is sequentially arranged with a slit, secondary Soller slit, anti-scattering slit, sealing box, monochromator, detector slit, and detector, allowing the diffracted light to be received. Step 4: Using X-ray diffraction conditions, the deformation between crystal planes is obtained, and the stress on the microscopic crystal is calculated. The stress on the microscopic crystal is: ——the angle between the vertical plane and the normal direction of the incident and outgoing rays, E——Young's modulus of the sample, v——Poisson's ratio of the sample, --different The distance between the crystal planes at the time of value, d0—— is the interplanar spacing of the crystal plane.

2. The cross-scale thin film stress testing method according to claim 1, characterized in that: In the step 1, the optical signal is converted into an amplified electrical signal and processed specifically by the line CCD.

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