Silicon wafer stress lossless non-contact measurement method and device

Abstract

The invention provides a silicon wafer stress lossless non-contact measurement method and device, and the method comprises the steps: generating a near-infrared femtosecond pulse; the optical power of the near-infrared femtosecond pulse is sufficient to penetrate through an object to be detected for imaging; enabling the near-infrared femtosecond pulse to penetrate through the to-be-measured object, applying stress to the interior of the to-be-measured object, and receiving a light pulse signal of transmission light; analyzing and reconstructing a light pulse signal of the transmission light, and constructing an interference image sequence penetrating through the to-be-detected object; and based on the interference image sequence of the to-be-measured object, determining a principal stress difference value at each point on the to-be-measured object. According to the invention, the stress condition of each point on the to-be-detected object can be accurately detected, and the problems that fixed-point measurement is difficult to realize and the number of detection frames is low in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement mechanics, and in particular to a method and device for non-destructive and non-contact measurement of silicon wafer stress. Background Art

[0002] Silicon wafers are the most commonly used substrate material for semiconductor device manufacturing. They are made from purified silicon and then go through processes such as roller milling, cutting, grinding, polishing, and cleaning. Due to silicon's brittleness and piezoresistive effect, silicon wafers can crack under stress, and their electrical properties can also significantly change. Therefore, stress in silicon wafers must be controlled as much as possible during semiconductor production and manufacturing. However, stress is unavoidable during various processes such as bonding, electroplating, and deposition. Therefore, a fast, non-destructive, and non-contact detection method is needed to measure stress in silicon wafers and further control it to prevent excessive stress from affecting the wafer.

[0003] Currently, semiconductor companies primarily use the Stoney method to measure silicon wafer stress. This method directly measures the curvature of the silicon wafer and then indirectly determines the stress caused by processes like electroplating and deposition using theoretical formulas. However, this method is not suitable for measuring stress in localized areas such as bonding points. Raman spectroscopy is commonly used to measure localized stress. This method offers high spatial resolution and allows for fixed-point measurement, but it can only measure surface stress, is slow, and cannot capture thermal stress caused by thermal mismatch in real time, making online measurement difficult.

[0004] There is currently no effective solution to the problems of difficulty in achieving fixed-point measurement and low detection frame rate in existing related technologies. Summary of the Invention

[0005] The present invention provides a non-destructive and non-contact measurement method and device for silicon wafer stress, which are used to solve the defects of the related technologies in the prior art, such as difficulty in achieving fixed-point measurement and low detection frame number.

[0006] In a first aspect, the present invention provides a method for non-destructive and non-contact measurement of silicon wafer stress, comprising: generating near-infrared femtosecond pulses, wherein the optical power of the near-infrared femtosecond pulses is sufficient to penetrate the object to be measured and form an image; allowing the near-infrared femtosecond pulse to pass through the object to be measured, applying stress to the interior of the object to be measured, and receiving an optical pulse signal of the transmitted light; Analyzing and reconstructing the optical pulse signal of the transmitted light to construct an interference image sequence passing through the object to be measured; Based on the interference image sequence of the object to be measured, the principal stress difference at each point on the object to be measured is determined.

[0007] According to a non-destructive and non-contact method for measuring silicon wafer stress provided by the present invention, before allowing the near-infrared femtosecond pulse to pass through the object to be measured, the method comprises: performing time domain stretching and power compensation on the near-infrared femtosecond pulse; Dispersing the near-infrared femtosecond pulse from a spatial light form into a one-dimensional spatial pulse form; The near-infrared femtosecond pulse is focused.

[0008] According to a non-destructive and non-contact method for measuring silicon wafer stress provided by the present invention, the optical pulse signal of the transmitted light is analyzed and reconstructed to construct an interference image sequence passing through the object to be measured, including: converting the optical pulse signal of the transmitted light into an analog electrical signal; The analog electrical signal is collected, and a two-dimensional light intensity distribution diagram sequence after passing through the object to be measured is restored.

[0009] According to the present invention, a non-destructive and non-contact method for measuring stress in a silicon wafer is provided, which determines the principal stress difference at each point on the object to be measured based on an interference image sequence of the object to be measured, including: determining, based on a sequence of two-dimensional light intensity distribution diagrams of the object to be measured, a phase difference generated by the transmitted light passing through each point of the object to be measured; Based on the phase difference generated by the transmitted light passing through each point of the object to be measured, the principal stress difference at each point of the object to be measured is determined.

[0010] According to a non-destructive and non-contact method for measuring silicon wafer stress provided by the present invention, the principal stress difference at each point of the object to be measured is determined based on the phase difference generated by the transmitted light passing through each point of the object to be measured, including: determining, based on the phase difference generated by the transmitted light passing through each point of the object to be measured, an optical path difference of two plane polarized lights split from the transmitted light along the principal stress direction of the object to be measured; The principal stress difference at each point of the object to be measured is determined based on the optical path difference.

[0011] According to a non-destructive and non-contact method for measuring silicon wafer stress provided by the present invention, the principal stress difference at each point of the object to be measured is determined based on the optical path difference, comprising: Determining, based on the optical path difference, a change in the refractive index of the object to be measured after stress is applied; Based on the linear relationship between the change in the refractive index of the object to be measured and the principal stress difference, the principal stress difference at each point of the object to be measured is determined.

[0012] In a second aspect, the present invention further provides a non-destructive and non-contact measurement device for silicon wafer stress, comprising: A near-infrared femtosecond laser for generating near-infrared femtosecond pulses, wherein the optical power of the near-infrared femtosecond pulses is sufficient to penetrate the object to be measured and form an image; a photodetector, configured to receive a light pulse signal of the transmitted light and convert the light pulse signal of the transmitted light into an analog electrical signal; A high-speed oscilloscope, used to collect and upload the analog electrical signal; The computer is used to construct an interference image sequence through the object to be measured according to the analog electrical signal; and determine the principal stress difference at each point on the object to be measured based on the interference image sequence of the object to be measured.

[0013] According to a non-destructive and non-contact measurement device for silicon wafer stress provided by the present invention, the measurement device further comprises a time domain stretching component, the time domain stretching component being arranged on the outgoing optical path of the near-infrared femtosecond laser, and being used to perform time domain stretching on the near-infrared femtosecond pulse; The measuring device also includes an optical signal amplification component and a spatial dispersion component; The optical signal amplification component is arranged on the outgoing optical path of the time domain stretching component, and is used to perform power compensation on the near-infrared femtosecond pulse; The spatial dispersion component is arranged on the outgoing light path of the optical signal amplification component, and is used to disperse the near-infrared femtosecond pulse from a spatial light form into a one-dimensional spatial pulse form.

[0014] According to a non-destructive and non-contact device for measuring stress in a silicon wafer provided by the present invention, the device further comprises a polarization control component and a scanning component; The polarization control component is used to control the polarization state of the spatial pulse incident on the object to be measured and passing through the object to be measured; The scanning component is used to realize scanning of the near-infrared femtosecond pulse on the object to be measured.

[0015] According to a non-destructive and non-contact silicon wafer stress measurement device provided by the present invention, the near-infrared femtosecond laser adopts a MHz-level near-infrared femtosecond laser, and the scanning component adopts a MHz-level acousto-optic deflector; The near-infrared femtosecond laser is used to generate near-infrared femtosecond pulses with a repetition frequency of MHz level; The acousto-optic deflector is used to enable the near-infrared femtosecond pulse to scan the object to be measured at a MHz rate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a non-destructive, non-contact method for measuring silicon wafer stress. By controlling laser power, the laser generates a near-infrared femtosecond pulse laser of a specific wavelength. After amplification, the laser has a specific power, allowing it to pass through the object under test, forming the image required for testing without damaging the object, thereby achieving non-contact, non-destructive testing. This method offers rapid measurement speed and requires no additional processing of the object under test, thus possessing the potential for online testing. It can also accurately measure stress at various points on the object under test, resolving the difficulties of achieving fixed-point measurement and the low detection frame rate encountered in existing related technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a flow chart of the non-destructive and non-contact measurement method for silicon wafer stress provided by the present invention; Figure 2 Schematic diagram of the non-destructive and non-contact stress measurement device for silicon wafers in Example 1 of the present invention; Figure 3 Schematic diagram of the non-destructive and non-contact measurement device for silicon wafer stress in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0020] Near-infrared light refers to electromagnetic waves with wavelengths between 780 and 2526 nm. While invisible to the human eye, it can be detected using sensors made of semiconductor materials such as InGaAs and HgCdTe. Due to the inherent properties of silicon, the absorption rate of light in this band is extremely low in the near-infrared band. Light incident on a silicon sample is mostly transmitted, with only a small portion reflected from the surface. Furthermore, the law of stress optics states that when a material is subjected to external stress, changes in the arrangement of atoms or molecules within it cause a change in the refractive index, leading to birefringence. The essence of this phenomenon is that the anisotropic stress distribution causes the material to produce different refractive indices for light with different polarization directions, resulting in a measurable optical path length difference or phase difference. Silicon crystals, which have a cubic unit cell with a diamond-like structure in the cubic system, normally do not exhibit birefringence. However, when external stress or internal stress is applied to silicon, the density and crystal structure of the silicon wafer at the stressed location change, altering its refractive index properties. This results in optical anisotropy, resulting in an anisotropic crystal. Although silicon wafers are not transparent to visible light, they are transparent to near-infrared light.

[0021] Based on this, the present invention provides a non-destructive and non-contact method for measuring silicon wafer stress. Figure 1 The flowchart of the non-destructive and non-contact measurement method for silicon wafer stress provided by the present invention is as follows: Figure 1 As shown, the method includes the following steps: Step S101, generating a near-infrared femtosecond pulse; the optical power of the near-infrared femtosecond pulse is sufficient to penetrate the object to be measured and form an image; Step S102, allowing a near-infrared femtosecond pulse to pass through the object to be measured, applying stress to the interior of the object to be measured, and receiving an optical pulse signal of the transmitted light; Step S103, analyzing and reconstructing the optical pulse signal of the transmitted light to construct an interference image sequence transmitted through the object to be measured; Step S104 : determining the principal stress difference at each point on the object to be measured based on the interference image sequence of the object to be measured.

[0022] In this method, a laser is first used to generate near-infrared femtosecond pulses of specific power and wavelength. Before the near-infrared femtosecond pulses reach the object to be tested, the power of the incident pulse is measured to ensure that the generated light power is sufficient to penetrate the object to be tested and is not too large to damage the object to be tested. The object to be tested can be a chip or other device. Then, the near-infrared femtosecond pulse is passed through the object to be tested, and stress is generated inside the object to be tested through electrical, thermal, and force means, and the light pulse signal of the transmitted light is received. The light pulse signal of the transmitted light is then analyzed and reconstructed to construct an interference image sequence passing through the object to be tested, with the frame rate equal to the repetition frequency of the laser. Finally, based on the interference image sequence of the object to be tested, the principal stress difference at each point on the object to be tested is determined. In the above process, by controlling the laser power, the near-infrared femtosecond pulse laser of a specific wavelength can be generated, and the laser has a specific power after amplification, so that the laser passes through the object to be tested and forms the image required for the test without damaging the object to be tested, thereby realizing non-contact non-destructive testing. This method has a fast measurement speed and does not require additional processing of the object to be measured. It has the potential for online detection and can accurately detect the stress conditions at each point on the object to be measured, solving the problems of difficulty in achieving fixed-point measurement and low detection frame rate in existing related technologies.

[0023] In some embodiments, step S102, before allowing the near-infrared femtosecond pulse to pass through the object to be measured, includes: time domain stretching and power compensation of the near-infrared femtosecond pulse; dispersing the near-infrared femtosecond pulse from a spatial light form to a one-dimensional spatial pulse form; and focusing the near-infrared femtosecond pulse.

[0024] In some embodiments, step S103 analyzes and reconstructs the optical pulse signal of the transmitted light to construct an interference image sequence passing through the object to be measured, including: converting the optical pulse signal of the transmitted light into an analog electrical signal; collecting the analog electrical signal, and restoring a two-dimensional light intensity distribution map sequence after passing through the object to be measured.

[0025] For example, a high-speed photodetector at or above the MHz level and a high-speed oscilloscope at or above the MHz level are used to receive the optical pulse signal of the transmitted light. The optical pulse signal is then analyzed and reconstructed to construct a sequence of interference images transmitted through the sample, with a frame rate equal to the repetition frequency of the laser.

[0026] On the basis of the above embodiment, step S104 determines the principal stress difference at each point on the object to be measured based on the interference image sequence of the object to be measured, including: determining the phase difference generated by the transmitted light passing through each point on the object to be measured based on the two-dimensional light intensity distribution map sequence of the object to be measured; and determining the principal stress difference at each point on the object to be measured based on the phase difference generated by the transmitted light passing through each point on the object to be measured.

[0027] Specifically, based on the phase difference generated when the transmitted light passes through each point of the object to be measured, the principal stress difference at each point of the object to be measured is determined, including: based on the phase difference generated when the transmitted light passes through each point of the object to be measured, determining the optical path difference of two plane polarized lights split along the principal stress direction of the object to be measured; and determining the principal stress difference at each point of the object to be measured based on the optical path difference.

[0028] More specifically, determining the principal stress difference at each point of the object to be measured based on the optical path difference includes: determining the change in the refractive index of the object to be measured after stress is applied based on the optical path difference; and determining the principal stress difference at each point of the object to be measured based on the linear relationship between the change in the refractive index of the object to be measured and the principal stress difference.

[0029] For example, the sampled optical pulse signal To the light intensity signal The conversion formula is as follows:

[0030] in, Represents the light intensity signal, represents the reference pulse intensity, Indicates the sampled optical pulse signal The filtered high-frequency component is the component after Hilbert transformation, and represent the real and imaginary parts respectively.

[0031] Then the phase difference generated by light after passing through the object to be measured with stress birefringence effect is:

[0032] in, represents the phase difference produced, represents the introduced spatially dependent phase, represents the phase difference introduced, Indicates the sampled optical pulse signal The filtered high-frequency component is the component after Hilbert transformation, and Therefore, by subtracting the phase images of the object under test with stress from the object under test without stress, the phase difference of each point inside the object under test can be obtained.

[0033] When stress exists inside the silicon wafer, the density and crystal structure of the stress position change, causing the refractive index of the silicon crystal to change, resulting in different refractive indices in the two principal stress directions. The incident plane polarized light will be decomposed into two plane polarized light beams with mutually perpendicular vibration directions along the two principal stress directions, and a certain optical path difference will be generated after passing through the silicon wafer. Assuming the wavelength is The linearly polarized light is incident vertically on the silicon wafer with a thickness of d, and the principal stress 、 The optical path difference of the two plane polarized lights split in the direction can be obtained by the following formula:

[0034] in, represents the optical path difference, Indicates the principal stress of the object to be measured along the incident light The refractive index of the direction, Indicates the principal stress of the object to be measured along with the incident light The propagation speed in the direction, Indicates the principal stress of the object to be measured along with the incident light The refractive index of the direction, Indicates the principal stress of the object to be measured along with the incident light The propagation speed in the direction, is the speed of light in vacuum, Indicates the thickness of the object to be measured.

[0035] When stress birefringence occurs, the change in the sample's refractive index is linearly related to the principal stress difference of the sample as follows:

[0036] in, Indicates the principal stress of the object to be measured along the incident light The refractive index of the direction, Indicates the principal stress of the object to be measured along the incident light The refractive index of the direction, is the stress optical constant, which is related to the properties of the object to be measured. Based on the above formula, we have:

[0037] In practical applications, the optical path difference can be obtained by measuring the phase difference. The specific formula is as follows:

[0038] in, represents the optical path difference, Indicates the principal stress of the object to be measured along the incident light The refractive index of the direction, Indicates the principal stress of the object to be measured along the incident light The refractive index of the direction, Indicates the thickness of the object to be measured, is the stress optical constant, represents the phase difference, represents the wavelength. Therefore, the difference between the two principal stresses on the object to be measured is:

[0039] in, represents the principal stress difference.

[0040] The present invention also provides a non-destructive and non-contact device for measuring silicon wafer stress, comprising: A near-infrared femtosecond laser is used to generate near-infrared femtosecond pulses; the optical power of the near-infrared femtosecond pulses is sufficient to penetrate the object to be measured and form an image; a photodetector, configured to receive a light pulse signal of the transmitted light and convert the light pulse signal of the transmitted light into an analog electrical signal; High-speed oscilloscope, used to collect and upload analog electrical signals; The computer is used to construct an interference image sequence through the object to be measured according to the analog electrical signal; based on the interference image sequence of the object to be measured, the principal stress difference at each point on the object to be measured is determined.

[0041] During use, a near-infrared femtosecond laser generates near-infrared femtosecond pulses of a first power and a first wavelength. Then, stress is generated within the object to be measured through electrical, thermal, or force-based means. Throughout the entire process, a MHz-class or higher high-speed photodetector and a MHz-class or higher high-speed oscilloscope are used to receive the transmitted light pulse signal and transmit it to the computer. The computer analyzes and reconstructs the light pulse signal, constructing an interference image sequence transmitted through the object to be measured, with a frame rate equal to the repetition frequency of the near-infrared femtosecond laser. Finally, based on the interference image sequence of the object to be measured, the phase difference and isoclinic angle of the object to be measured are obtained, and the principal stress difference at each point on the object to be measured is determined.

[0042] In some embodiments, the measuring device further includes a time domain stretching component, which is disposed on an outgoing optical path of the near-infrared femtosecond laser and is used to perform time domain stretching on the near-infrared femtosecond pulse.

[0043] Furthermore, the measuring device also includes an optical signal amplification component and a spatial dispersion component; the optical signal amplification component is arranged on the output optical path of the time domain stretching component, and is used to perform power compensation on the near-infrared femtosecond pulse; the spatial dispersion component is arranged on the output optical path of the optical signal amplification component, and is used to disperse the near-infrared femtosecond pulse from a spatial light form into a one-dimensional spatial pulse form.

[0044] Exemplarily, the spatial dispersion component uses a diffraction grating, which is used to disperse the laser pulse into one-dimensional spatial pulses, so that they can be mapped to different positions on the object to be measured.

[0045] In some embodiments, the measuring device further includes a polarization control component and a scanning component; the polarization control component is used to control the polarization state of the spatial pulse incident on the object to be measured and passing through the object to be measured; the scanning component is used to realize the scanning of the near-infrared femtosecond pulse on the object to be measured.

[0046] The polarization control assembly includes a first polarization control assembly and a second polarization control assembly. The first polarization control assembly is located in the outgoing optical path of the spatial dispersion assembly and is used to control and change the polarization state of the spatial pulse when it is incident on the object to be measured. The second polarization control assembly is located in the outgoing optical path of the scanning assembly and is used to control and change the polarization state of the spatial pulse after it passes through the object to be measured. Both the first and second polarization control assemblies utilize a combination of a linear polarizer and a wave plate. The linear polarizer converts unpolarized laser light into linearly polarized light, while the wave plate changes the polarization direction of the polarized light.

[0047] In some embodiments, the measurement device further includes a collimator positioned between the optical signal amplification component and the spatial dispersion component. The collimator is configured to direct the pulses amplified by the optical signal amplification component into the spatial dispersion component at a specific angle and in the form of spatial light. The collimator is also positioned between the second polarization control component and the high-speed photodetector. The collimator is configured to couple the pulses transmitted through the object to be measured into the optical path for detection by the high-speed photodetector.

[0048] Furthermore, the measuring device also includes a first lens combination and a second lens combination; the first lens combination is arranged between the spatial dispersion component and the first polarization control component, and the first lens combination is used to adjust the size of the spatial pulse spot and adjust the angle of the pulse incident on the first polarization control component and the scanning component; the second lens combination is arranged between the exit side of the object to be measured and the second polarization control component, and the second lens combination is used to converge the transmitted pulse onto the second polarization control component.

[0049] This device uses ultrafast laser imaging, with a temporal resolution comparable to the laser's pulse repetition frequency, reaching the MHz level. By selecting different scanning components, it is possible to scan a wide range of the object under test, from a small point to the entire surface. The imaging frame rate is also limited by the scanning components. Using high-speed scanning components such as acousto-optic deflectors (AODs) for multi-point or small-range scanning can achieve a frame rate of 0.1 MHz. Furthermore, this device uses infrared ultrafast laser imaging. Due to the infrared laser's penetrability into silicon materials, by setting the scanning range, the resulting image sequence contains refractive index information for the entire or local silicon wafer under test. After the images are processed by the described algorithm, the stress distribution of the entire or local silicon wafer under test can be reflected.

[0050] The following is an example of the above device: Example 1: Figure 2 Schematic diagram of the non-destructive non-contact stress measurement device for silicon wafers in Example 1 of the present invention. Figure 2As shown, the device includes: a near-infrared femtosecond laser 101, a single-mode optical fiber 102, an erbium-doped fiber amplifier 103, a first collimator 104, a first diffraction grating 105, a first focusing lens group 106, a first polarizer 107, a first wave plate 108, a two-dimensional scanning galvanometer 109, a scanning lens 110, a sample holder 111, a second focusing lens group 112, a second polarizer 113, a second wave plate 114, a second collimator 115, a MHz-level or higher high-speed photodetector 116, a MHz-level or higher high-speed oscilloscope 117, and a computer 118.

[0051] Among them, the near-infrared femtosecond laser 101 is connected to the single-mode optical fiber 102, the erbium-doped fiber amplifier 103 is connected to the single-mode optical fiber 102, the first collimator 104 is connected to the erbium-doped fiber amplifier 103, the first diffraction grating 105 is located in front of the first collimator 104, the first focusing lens group 106 is located in front of the first diffraction grating 105, the first polarizer 107 and the first wave plate 108 are located in front of the first focusing lens group 106, the two-dimensional scanning galvanometer 109 is located in front of the first polarizer 107 and the first wave plate 108, and the two-dimensional scanning galvanometer 109, the scanning lens 110, the object to be measured, the second focusing lens group 112, the second polarizer 113, the second wave plate 114, and the second collimator 115 are located on the same optical axis. A MHz-level or higher high-speed photodetector 116 is connected to the second collimator 115 , a MHz-level or higher high-speed oscilloscope 117 is connected to the MHz-level or higher high-speed free-space photodetector 116 , and a computer 118 is connected to the MHz-level or higher high-speed oscilloscope 117 .

[0052] The specific steps when using the device are as follows: Step 1: Fix the object to be measured on the sample holder 111 of the measuring device.

[0053] Step 2: During calibration, the optical power meter is positioned between the scanning lens 110 and the object to be measured, and the near-infrared femtosecond laser 101 and the erbium-doped fiber amplifier 103 are adjusted so that the generated femtosecond laser pulse has a first power and a first wavelength after amplification, wherein the power is sufficient to penetrate the object to be measured without damaging the object to be measured, and the wavelength is sufficient to form an image of sufficient quality after penetrating the silicon and other polymer components of the object to be measured; after the test begins, the optical power meter is removed from the optical path, and the pulse power and wavelength emitted and amplified by the femtosecond laser 101 and the erbium-doped fiber amplifier 103 are kept unchanged. Step 3: Time-stretching the femtosecond laser pulse through the single-mode optical fiber 102. The time-stretched pulse is incident on the first diffraction grating 105 at a specific angle in the form of spatial light through the first collimator 104. Step 4: The spatial pulse is dispersed into one-dimensional spatial pulses by the first diffraction grating 105, focused by the first focusing lens group 106, converted into polarized light with a specific polarization through the first polarizer 107 and the first wave plate 108, and then focused on different positions on the object to be measured through the two-dimensional galvanometer group 109 and the scanning lens 110, thereby realizing a large-scale two-dimensional scanning of the object to be measured by the one-dimensional femtosecond laser.

[0054] Step 5: The pulse passing through the object to be measured passes through the second focusing lens group 112, the second polarizer 113 and the second wave plate 114, and is coupled to the MHz-level or above high-speed photodetector 116 via the second collimator 115.

[0055] Step 6: The transmitted pulse is converted into an analog electrical signal via a high-speed photodetector, and is sampled into a computer 118 via a MHz-level or higher high-speed oscilloscope 117 .

[0056] Step 7: The computer 118 recovers the two-dimensional light intensity distribution sequence after passing through the object using the signal sampled by the MHz-class or higher high-speed oscilloscope 117. The frame rate is limited by the scanning rate of the two-dimensional galvanometer group.

[0057] Step 8: Restore the above light intensity distribution sequence to obtain the phase difference generated by the light after passing through the sample with stress birefringence effect. The distribution matrix of each point on the object to be measured.

[0058] Step 9: For the above phase difference The principal stress difference at each point on the sample is calculated by the distribution matrix of .

[0059] Example 2: Figure 3 Schematic diagram of the non-destructive non-contact measurement device for silicon wafer stress in Example 2 of the present invention. Figure 3 As shown, the device includes: a near-infrared femtosecond laser 201, a single-mode optical fiber 202, an erbium-doped fiber amplifier 203, a first collimator 204, a first polarizer 205, a first wave plate 206, a first polarization beam splitter 207, an acousto-optic deflector 208, a first diffraction grating 209, a beam expander 210, a first scanning lens 211, a second scanning lens 212, a beam combiner 213, a second diffraction grating 214, a second wave plate 215, a second polarization beam splitter 216, a reflector 217, a third wave plate 218, an acousto-optic modulator 219, a delay mirror 220, a shaping mirror 221, a fourth wave plate 222, a focusing lens 223, a second collimator 224, a MHz-level or higher high-speed photodetector 225, a MHz-level or higher high-speed oscilloscope 226, and a computer 227.

[0060] The near-infrared femtosecond laser 201 is connected to a single-mode fiber 202, the erbium-doped fiber amplifier 203 is connected to the single-mode fiber 202, and the first collimator 204 is connected to the erbium-doped fiber amplifier 203. The first polarizer 205, the first wave plate 206, the transmission side of the first polarization beam splitter 207, and the acousto-optic deflector 208 are located on the same optical axis. The first diffraction grating 209 is located at the output light of the acousto-optic deflector 208. The first diffraction grating 209, the beam expander 210, the first scanning lens 211, the second scanning lens 212, the beam combiner 213, and the second diffraction grating 214 are also located on the same optical axis. The light emitted from the second diffraction grating 214 also lies on the same optical axis as the second wave plate 215, the second polarization beam splitter 216, the focusing lens assembly 223, and the second collimator 224. The reflector 217 is located on the reflection side of the first polarization beam splitter 207 and on the same optical axis as the third wave plate 218 and the acousto-optic modulator 219. The delay lens assembly 220 is located on the output side of the acousto-optic modulator 219, and the light emitted from the delay lens assembly 220 lies on the same optical axis as the shaping lens assembly 221, the fourth wave plate 222, and the second polarization beam splitter 216. A MHz-class or higher high-speed photodetector 225 is connected to the second collimator 224. A MHz-class or higher high-speed oscilloscope 226 is connected to the MHz-class or higher high-speed free-space photodetector 225. A computer 227 is connected to the MHz-class or higher high-speed oscilloscope 226.

[0061] The specific steps when using the device are as follows: Step 1: Fix the object to be measured on the fixing frame of the measuring device.

[0062] Step 2: During calibration, the optical power meter is positioned between the scanning lens and the object to be measured. The femtosecond laser 201 and the erbium-doped fiber amplifier 203 are adjusted so that the generated femtosecond laser pulse has a first power and a first wavelength after amplification. The power is sufficient to penetrate the object to be measured without damaging the object to be measured, and the wavelength is sufficient to form an image of sufficient quality after penetrating the silicon and other polymer components of the object to be measured. After the test begins, the optical power meter is removed from the optical path, and the power and wavelength of the pulses emitted and amplified by the femtosecond laser 201 and the erbium-doped fiber amplifier 203 remain unchanged.

[0063] Step 3: Time-domain stretching is performed on the femtosecond laser pulse through the single-mode optical fiber 202. The time-domain stretched pulse is incident on the first polarizer 205 and the first wave plate 206 at a specific angle and in the form of spatial light through the first collimator 204, thereby becoming polarized light with a specific polarization direction.

[0064] Step 4: The polarized light is split into two beams, sample light and reference light, via the first polarization beam splitter 207. The sample light is deflected by the acousto-optic deflector 208 and irradiated onto the first diffraction grating 209. It is then focused onto different positions on the object to be measured via the beam expander 210 and the first scanning lens 211, thereby achieving large-scale two-dimensional scanning of the object to be measured by the one-dimensional femtosecond laser. The reference light is phase-shifted by the reflector 217 and the third wave plate 218 before being modulated by the acousto-optic modulator 219. It is then delayed by the delay mirror 220 and shaped by the shaping mirror 221. It is then phase-shifted again by the fourth wave plate 222 before being incident on the second polarization beam splitter 216.

[0065] Step 5: The pulse of sample light passing through the object to be measured passes through the beam combining lens group 213, the second diffraction grating 214 and the second wave plate 215, is combined with the reference light path through the second polarization beam splitter 216, and is then coupled into the high-speed photodetector 225 through the focusing lens group 223 and the second collimator 224.

[0066] Step 6: The combined pulse is converted into an analog electrical signal via a high-speed photodetector 225 , and is sampled by a MHz-level or higher high-speed oscilloscope 226 and then transferred to a computer 227 .

[0067] Step 7: The computer 227 recovers the two-dimensional light intensity distribution sequence after passing through the object by sampling the signal obtained by the MHz-level or higher high-speed oscilloscope 226 . The frame rate of the sequence is limited by the scanning rate of the acousto-optic deflector 208 .

[0068] Step 8: Restore the above light intensity distribution sequence to obtain the phase difference generated by the light after passing through the object to be measured with stress birefringence effect. The distribution matrix of each point on the object to be measured.

[0069] Step 9: For the above phase difference The principal stress difference at each point on the sample is calculated by the distribution matrix of .

[0070] The two aforementioned examples leverage the femtosecond nature of near-infrared femtosecond laser pulses and their ability to penetrate silicon. They employ a diffraction grating, a two-dimensional galvanometer, and an acousto-optic deflector to disperse the spatial pulses, forming a two-dimensional scan of the surface of the object being measured. This allows for ultrafast acquisition of the light intensity distribution after the pulses pass through the object. Combined with the aforementioned algorithm based on stress-optics laws, the stress distribution of the object, either global or local, can be calculated. The entire measurement process is contactless, enabling ultrafast, non-destructive, and non-contact stress measurement of the object with high temporal resolution and the potential for online testing.

[0071] Compared with Example 1, Example 2 uses an acousto-optic deflector 208 as a scanning component. The acousto-optic deflector 208 is an acousto-optic element with a fast scanning frequency. The one-dimensional scanning rate can reach 107 The frequency is on the order of Hz, far higher than the galvanometer solution used in Example 1. There is no inertia or noise caused by mechanical motion during scanning, but the corresponding field of view is relatively limited. Furthermore, the acousto-optic deflector 208 is a polarization-sensitive element, requiring the incident light to have a certain polarization state. Therefore, corresponding polarizer and analyzer components must be added to the optical path, making the optical path more complex.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A non-destructive and non-contact method for measuring silicon wafer stress, characterized in that: include: Producing near-infrared femtosecond pulses; The optical power of the near-infrared femtosecond pulse is sufficient to penetrate the object to be measured and form an image; allowing the near-infrared femtosecond pulse to pass through the object to be measured, applying stress to the interior of the object to be measured, and receiving an optical pulse signal of the transmitted light; Analyzing and reconstructing the optical pulse signal of the transmitted light to construct an interference image sequence passing through the object to be measured; Based on the interference image sequence of the object to be measured, the principal stress difference at each point on the object to be measured is determined.

2. The non-destructive and non-contact measurement method for silicon wafer stress according to claim 1, characterized in that: Before allowing the near-infrared femtosecond pulse to pass through the object to be measured, the method includes: performing time domain stretching and power compensation on the near-infrared femtosecond pulse; Dispersing the near-infrared femtosecond pulse from a spatial light form into a one-dimensional spatial pulse form; The near-infrared femtosecond pulse is focused.

3. The non-destructive and non-contact stress measurement method for silicon wafers according to claim 1, characterized in that: Analyzing and reconstructing the optical pulse signal of the transmitted light to construct an interference image sequence passing through the object to be measured, including: converting the optical pulse signal of the transmitted light into an analog electrical signal; The analog electrical signal is collected, and a two-dimensional light intensity distribution diagram sequence after passing through the object to be measured is restored.

4. The non-destructive and non-contact method for measuring silicon wafer stress according to claim 3, wherein: Determining the principal stress difference at each point on the object to be measured based on the interference image sequence of the object to be measured includes: determining, based on a sequence of two-dimensional light intensity distribution diagrams of the object to be measured, a phase difference generated by the transmitted light passing through each point of the object to be measured; Based on the phase difference generated by the transmitted light passing through each point of the object to be measured, the principal stress difference at each point of the object to be measured is determined.

5. The non-destructive and non-contact method for measuring silicon wafer stress according to claim 4, wherein: Determining the principal stress difference at each point of the object to be measured based on the phase difference generated by the transmitted light passing through each point of the object to be measured includes: determining, based on the phase difference generated by the transmitted light passing through each point of the object to be measured, an optical path difference of two plane polarized lights split from the transmitted light along the principal stress direction of the object to be measured; The principal stress difference at each point of the object to be measured is determined based on the optical path difference.

6. The non-destructive and non-contact method for measuring silicon wafer stress according to claim 5, characterized in that: Determining the principal stress difference at each point of the object to be measured based on the optical path difference includes: Determining, based on the optical path difference, a change in the refractive index of the object to be measured after stress is applied; Based on the linear relationship between the change in the refractive index of the object to be measured and the principal stress difference, the principal stress difference at each point of the object to be measured is determined.

7. A non-destructive and non-contact measurement device for silicon wafer stress, characterized in that: include: Near-infrared femtosecond laser, used to generate near-infrared femtosecond pulses; The optical power of the near-infrared femtosecond pulse is sufficient to penetrate the object to be measured and form an image; a photodetector, configured to receive a light pulse signal of the transmitted light and convert the light pulse signal of the transmitted light into an analog electrical signal; A high-speed oscilloscope, used to collect and upload the analog electrical signal; A computer, configured to construct an interference image sequence through the object to be measured based on the analog electrical signal; Based on the interference image sequence of the object to be measured, the principal stress difference at each point on the object to be measured is determined.

8. The non-destructive and non-contact measurement device for silicon wafer stress according to claim 7, characterized in that: The measuring device further includes a time domain stretching component, which is arranged on the outgoing optical path of the near-infrared femtosecond laser and is used to perform time domain stretching on the near-infrared femtosecond pulse; The measuring device also includes an optical signal amplification component and a spatial dispersion component; The optical signal amplification component is arranged on the outgoing optical path of the time domain stretching component, and is used to perform power compensation on the near-infrared femtosecond pulse; The spatial dispersion component is arranged on the outgoing light path of the optical signal amplification component, and is used to disperse the near-infrared femtosecond pulse from a spatial light form into a one-dimensional spatial pulse form.

9. The non-destructive and non-contact measurement device for silicon wafer stress according to claim 8, characterized in that: The measuring device further comprises a polarization control component and a scanning component; The polarization control component is used to control the polarization state of the spatial pulse incident on the object to be measured and passing through the object to be measured; The scanning component is used to realize scanning of the near-infrared femtosecond pulse on the object to be measured.

10. The non-destructive and non-contact measurement device for silicon wafer stress according to claim 9, characterized in that: The near-infrared femtosecond laser adopts a MHz-level near-infrared femtosecond laser, and the scanning component adopts a MHz-level acousto-optic deflector; The near-infrared femtosecond laser is used to generate near-infrared femtosecond pulses with a repetition frequency of MHz level; The acousto-optic deflector is used to enable the near-infrared femtosecond pulse to scan the object to be measured at a MHz rate.

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