An optical signal conditioning device and wafer defect detection device

Abstract

The utility model discloses a kind of optical signal adjusting device and wafer defect detection device, it is related to semiconductor detection technical field.Optical signal adjusting device includes: photoelectric detector, ADC sampling circuit, processor, digital-analog conversion module and high voltage module.Photoelectric detector is converted into electric signal after the scattered light signal generated by wafer being irradiated by laser;Photoelectric detector is connected with processor by ADC sampling circuit, so that processor can be based on the digital signal of sampling circuit acquisition generation signal envelope, and then according to whether the curvature variation of signal envelope exceeds threshold to determine whether wafer has defect.Processor is connected with the input end of photoelectric detector by digital-analog conversion module, high voltage module in turn.For the case of determining that wafer has defect, can be through digital-analog conversion module and high voltage module, realize the adjustment of photoelectric detector gain, i.e.it is realized to the regulation of scattered light signal, avoid scattered light overexposure, to improve the accuracy of wafer defect detection.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor testing technology, and in particular to an optical signal conditioning device and a wafer defect detection device. Background Technology

[0002] Semiconductor inspection technology plays a crucial role in the semiconductor manufacturing process, with wafer defect detection being a key aspect. During inspection, after a laser illuminates the wafer, the interaction between the laser and the wafer generates scattered light signals. If this scattered light is overexposed, it can mask defects, leading to a decrease in the accuracy of wafer defect detection.

[0003] Therefore, improving the accuracy of wafer defect detection is a technical problem that urgently needs to be solved by those in this field. Utility Model Content

[0004] The purpose of this invention is to provide an optical signal conditioning device and a wafer defect detection device to solve the technical problem that when the scattered light signal generated after the interaction between the laser and the wafer is overexposed, it will cover up the defects, leading to a decrease in the accuracy of wafer defect detection.

[0005] In a first aspect, this application provides an optical signal conditioning device, comprising: a photodetector, an ADC sampling circuit, a processor, a digital-to-analog converter (DAC), and a high-voltage module. The first input terminal of the photodetector receives the scattered light signal generated after the wafer is irradiated by a laser, and converts the scattered light signal into an electrical signal. The output terminal of the photodetector is connected to the input terminal of the ADC sampling circuit, and the output terminal of the ADC sampling circuit is connected to the input terminal of the processor. This allows the processor to generate a signal envelope based on the digital signal acquired by the sampling circuit, and then determine whether the wafer has a defect based on whether the curvature change of the signal envelope exceeds a threshold. The output terminal of the processor is connected to the input terminal of the DAC module; the output terminal of the DAC module is connected to the input terminal of the high-voltage module; and the output terminal of the high-voltage module is connected to the second input terminal of the photodetector. This allows for adjustment of the photodetector gain by connecting the DAC module and the high-voltage module, which are sequentially connected to the processor, when a wafer defect is determined to be present. This adjustment reduces the occurrence of overexposure of the scattered light, thereby improving the accuracy of wafer defect detection.

[0006] In one possible implementation, the optical signal conditioning device further includes a current-to-voltage conversion module. The output of the photodetector is connected to the input of the ADC sampling circuit via the current-to-voltage conversion module. The weak current output by the photodetector can be converted into a easily processed voltage signal by the current-to-voltage conversion module, and the signal can also be amplified to improve the signal-to-noise ratio; then, when connected to the ADC sampling circuit, the analog voltage can be accurately converted into a digital signal, facilitating subsequent data acquisition and processing in the system, and making signal transmission and analysis more stable and reliable.

[0007] In one possible implementation, the optical signal conditioning device further includes a low-pass filter. The current-to-voltage conversion module is connected to the input of the ADC sampling circuit via the low-pass filter. The low-pass filter processes the raw signal acquired by the photodetector, retaining only the envelope information. This reduces the requirements for envelope sampling by the ADC, allowing for the selection of an ADC with a higher quantization bit depth to improve envelope sampling accuracy and thus enhance detection accuracy.

[0008] In one possible implementation, the low-pass filter is a low-pass filter hardware circuit or an external low-pass filter, which can filter out high-frequency interference signals in advance; at the same time, it does not require the CPU to participate in the filtering operation and does not occupy system resources.

[0009] In one possible implementation, the low-pass filter can be an active filter or a passive filter. Passive filters are simple in structure, low in cost, and highly reliable, and can operate without a power supply; active filters offer superior filtering performance, providing gain and strong load capacity. Using either an active or passive low-pass filter allows for flexible selection of the low-pass filter.

[0010] In one possible implementation, the low-pass filter is an active filter, which can be an elliptic filter, a Butterworth filter, or a Chebyshev filter. Active filters can amplify signals through built-in operational amplifiers or other active devices, enhancing useful signals without the need for additional amplification modules while effectively suppressing noise; moreover, they have extremely low output impedance, easily driving subsequent circuits and avoiding attenuation and distortion during signal transmission.

[0011] In one possible implementation, the low-pass filter is a 5th-order Chebyshev filter. At the same order, a 5th-order Chebyshev filter has a steeper transition band than a Butterworth filter, allowing for a faster transition from the passband to the stopband; it is less sensitive to changes in component parameters and exhibits better stability; and compared to higher-order filters, it requires fewer components to meet filtering performance requirements, thus simplifying circuit design.

[0012] In one possible implementation, a photomultiplier tube is used as a photodetector, which has extremely strong optical signal amplification capabilities, can convert weak light signals into measurable electrical signals, and has extremely high detection sensitivity, making it suitable for capturing extremely weak light scenes.

[0013] In one possible implementation, the transimpedance amplifier, as a current-to-voltage conversion module, can directly and accurately convert weak current signals into easily measurable voltage signals without the need for additional complex circuitry; it features low noise, fast response speed, effectively reduces signal distortion, and maintains stable conversion performance over a wide frequency range, making it suitable for various weak current detection scenarios.

[0014] Secondly, this application provides a wafer defect detection device, including: a laser source and the aforementioned optical signal conditioning device, wherein the laser source is used to emit laser light to irradiate the wafer. It has the same beneficial effects as the aforementioned optical signal conditioning device. Attached Figure Description

[0015] To more clearly illustrate the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of an optical signal conditioning device provided in an embodiment of this application;

[0017] Figure 2 This is a schematic diagram of another optical signal conditioning device provided in an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures:

[0019] 1-Photodetector;

[0020] 2- ADC sampling circuit;

[0021] 3-Processor;

[0022] 4-Digital-to-analog conversion module;

[0023] 5-High voltage module;

[0024] 6-Current-to-Voltage Conversion Module;

[0025] 7-Low-pass filter device. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0027] During wafer defect detection, the wafer is positioned on a displacement stage, and a laser emitted from a laser source illuminates the wafer surface, generating a scattered light signal. To adjust this scattered light signal, this application proposes an optical signal adjustment device. It is worth noting that the optical signal adjustment device provided in this application is primarily used in wafer defect detection scenarios for semiconductor equipment, but it can also be extended to other scenarios requiring laser power adjustment.

[0028] Example 1

[0029] Figure 1 This is a schematic diagram of an optical signal conditioning device provided in an embodiment of this application, as shown below. Figure 1 As shown, the device includes: a photodetector 1, an ADC sampling circuit 2, a processor 3, a digital-to-analog converter module 4, and a high-voltage module 5.

[0030] The first input terminal of photodetector 1 is used to receive the scattered light signal generated after the wafer is irradiated by laser; the output terminal of photodetector 1 is connected to the input terminal of ADC sampling circuit 2.

[0031] The output of ADC sampling circuit 2 is connected to the input of processor 3; the output of processor 3 is connected to the input of digital-to-analog converter module 4.

[0032] The output terminal of the digital-to-analog converter module 4 is connected to the input terminal of the high-voltage module 5; the output terminal of the high-voltage module 5 is connected to the second input terminal of the photodetector 1.

[0033] The photodetector 1 utilizes the photoelectric effect to convert incident light signals into detectable electrical signals. When photons strike the sensitive material of the detector, they interact with electrons within the material. If the photon energy is sufficient, it causes electrons to detach from the material surface or alters the internal carrier distribution, thereby changing the material's conductivity or generating an electromotive force, ultimately achieving the light-to-electric signal conversion. The photodetector 1 used is not limited and can be a photodiode, photomultiplier tube, etc. Because photomultiplier tubes possess extremely strong internal signal amplification capabilities, they can detect extremely weak light signals at the single-photon level, while ordinary photodiodes lack signal amplification and have much lower sensitivity to weak light. Therefore, to improve detection accuracy, the photodetector 1 in this embodiment is a photomultiplier tube.

[0034] The output of photodetector 1 is connected to the input of ADC sampling circuit 2 (where ADC is short for Analog-to-Digital Converter). ADC sampling circuit 2 mainly consists of signal conditioning, sample-and-hold, quantization, and encoding modules. During operation, the input analog signal is first optimized by the conditioning circuit, then the sample-and-hold circuit locks the signal value at a specific time, the quantization module converts the analog value into a discrete digital quantity, and finally the encoding module converts the digital quantity into binary or other codes that can be recognized by processor 3.

[0035] To improve signal processing accuracy, the optical signal conditioning device also includes a current-to-voltage conversion module 6. The output terminal of the photodetector 1 is connected to the input terminal of the ADC sampling circuit 2 via the current-to-voltage conversion module 6. The weak current output by the photodetector 1 can be converted into a easily processed voltage signal by the current-to-voltage conversion module 6, and the signal can also be amplified to improve the signal-to-noise ratio. The current-to-voltage conversion module 6 used is not limited; for example, a resistor can be connected in series between the photodetector 1 and the ADC sampling circuit 2, directly converting the current flow into voltage. To improve response speed and reduce noise, in one possible implementation, the current-to-voltage conversion module 6 is a transimpedance amplifier. Using a transimpedance amplifier as the current-to-voltage conversion module 6 can directly and accurately convert weak current signals into easily measurable voltage signals without the need for additional complex circuitry; it features low noise, fast response speed, effectively reduces signal distortion, and maintains stable conversion performance over a wide frequency range, making it suitable for various weak current detection scenarios.

[0036] The output of the ADC sampling circuit 2 is connected to the input of the processor 3, sending a string of digital codes corresponding to the analog voltage input to the ADC sampling circuit 2 to the processor 3 for processing. The processor 3 used is not limited; it can be a central processing unit (CPU) or a field-programmable gate array (FPGA).

[0037] Processor 3 generates a signal envelope based on the light intensity digital signal, and then obtains information such as defect size and shape based on the signal envelope to realize defect detection of the wafer.

[0038] Scattered light signals are generated after the laser interacts with the wafer. If the scattered light is overexposed, it will mask defects, leading to a decrease in the accuracy of wafer defect detection. Therefore, in this application, the output terminal of the processor 3 is connected to the input terminal of the digital-to-analog converter module 4, the output terminal of the digital-to-analog converter module 4 is connected to the input terminal of the high-voltage module 5, and the output terminal of the high-voltage module 5 is connected to the second input terminal of the photodetector 1.

[0039] The digital-to-analog conversion module 4 (such as a digital-to-analog converter) and the high-voltage module 5 are used to adjust the gain value of the photodetector 1. The digital-to-analog conversion module 4 converts the discrete binary values ​​of the digital signal into continuously changing analog voltage or current signals through circuits such as resistor networks.

[0040] The output of the digital-to-analog converter module 4 is connected to the input of the high-voltage module 5.

[0041] Photodetector 1 converts light signals into electrical signals; gain essentially amplifies the converted electrical signal. Adjusting the gain involves changing the detector's bias voltage (output by the high-voltage module 5 described above) or the parameters of its internal amplification circuit, thus allowing light signals of the same intensity to generate electrical signals of different amplitudes. Taking photodetector 1 as a photomultiplier tube (PMT) as an example, the PMT contains multiple dynodes. A voltage difference is applied between each stage, causing electrons to accelerate and collide with the dynodes in an electric field, generating more secondary electrons. Increasing the voltage between the dynodes significantly improves the secondary electron emission efficiency of each stage. As the electron emission efficiency increases, the output current increases accordingly, thereby increasing the gain. The PMT uses an external high-voltage module 5 to provide the interstage voltage. By adjusting the output voltage of the high-voltage module 5, the overall operating voltage of the PMT is controlled, thereby changing the interstage voltage and achieving the goal of adjusting the PMT's gain.

[0042] Increasing the gain amplifies weak light signals more significantly, resulting in a stronger output electrical signal; decreasing the gain reduces the amplification of strong light signals, preventing output signal overload. Therefore, when scattered light is overexposed, reducing the gain of photodetector 1 decreases the amplification intensity of the scattered light, thus preventing overexposure and improving the accuracy of wafer defect detection.

[0043] The optical signal conditioning device provided in this embodiment includes: a photodetector 1, an ADC sampling circuit 2, a processor 3, a digital-to-analog converter module 4, and a high-voltage module 5. The first input terminal of the photodetector 1 receives the scattered light signal generated after the wafer is irradiated by a laser and converts the scattered light signal into an electrical signal. The output terminal of the photodetector 1 is connected to the input terminal of the ADC sampling circuit 2, and the output terminal of the ADC sampling circuit 2 is connected to the input terminal of the processor 3. This allows the processor 3 to generate a signal envelope based on the digital signal acquired by the sampling circuit, and then determine whether the wafer has defects based on whether the curvature change of the signal envelope exceeds a threshold. The output terminal of the processor 3 is connected to the input terminal of the digital-to-analog converter module 4; the output terminal of the digital-to-analog converter module 4 is connected to the input terminal of the high-voltage module 5; and the output terminal of the high-voltage module 5 is connected to the second input terminal of the photodetector 1. This allows the gain of the photodetector 1 to be adjusted by connecting the digital-to-analog converter module 4 and the high-voltage module 5, which are connected to the processor 3 in sequence. This adjustment of the scattered light signal reduces overexposure of the scattered light and improves the accuracy of wafer defect detection. Furthermore, the signal conditioning device also includes a current-to-voltage conversion module 6. The output of the photodetector 1 is connected to the input of the ADC sampling circuit 2 through the current-to-voltage conversion module 6. The weak current output by the photodetector 1 can be converted into an easily processed voltage signal by the current-to-voltage conversion module 6, and the signal can also be amplified to improve the signal-to-noise ratio. Then, when connected to the ADC sampling circuit 2, the analog voltage can be accurately converted into a digital signal, which facilitates data acquisition and processing in subsequent systems, making signal transmission and analysis more stable and reliable. In addition, the selection of a transimpedance amplifier as the current-to-voltage conversion module 6 can directly and accurately convert the weak current signal into an easily measurable voltage signal without the need for additional complex circuits. It has low noise, fast response speed, can effectively reduce signal distortion, and can maintain stable conversion performance over a wide frequency range, making it suitable for various weak current detection scenarios.

[0044] Example 2

[0045] Since the laser repetition rate is in the tens of MHz, and the signal width sampled by photodetector 1 is only a few ns, an ADC with a sampling rate of Gsps or higher is required to accurately recover the envelope. The large amount of acquired data (tens of Gbps) and the abundance of invalid data necessitate high resource requirements for post-processing. Therefore, based on the above embodiments, the optical signal conditioning device provided in this application further includes a low-pass filter 7. The current-to-voltage conversion module 6 is connected to the input terminal of the ADC sampling circuit 2 through the low-pass filter 7. Figure 2 This is a schematic diagram of another optical signal conditioning device provided in an embodiment of this application, as shown below. Figure 2 As shown, the optical signal conditioning device includes: a photodetector 1, a current-to-voltage conversion module 6, a low-pass filter 7, an ADC sampling circuit 2, a processor 3, a digital-to-analog conversion module 4, and a high-voltage module 5.

[0046] The first input terminal of photodetector 1 is used to receive the scattered light signal generated after the wafer is irradiated by laser; the output terminal of photodetector 1 is connected to the input terminal of current-to-voltage conversion module 6, the output terminal of current-to-voltage conversion module 6 is connected to the input terminal of low-pass filter device 7, the output terminal of low-pass filter device 7 is connected to the input terminal of ADC sampling circuit 2, the output terminal of ADC sampling circuit 2 is connected to the input terminal of processor 3, the output terminal of processor 3 is connected to the input terminal of digital-to-analog conversion module 4, the output terminal of digital-to-analog conversion module 4 is connected to the input terminal of high voltage module 5, and the output terminal of high voltage module 5 is connected to the second input terminal of photodetector 1.

[0047] The optical signal conditioning device provided in this embodiment is the same as the optical signal conditioning device provided in Embodiment 1. Please refer to the description above, which will not be repeated here. The difference between Embodiment 2 and Embodiment 1 is the addition of a low-pass filter device 7.

[0048] The signal output from the current-to-voltage conversion module 6 is processed by the low-pass filter 7. The signal after passing through the low-pass filter 7 retains only the envelope information, which reduces the specification requirements for the ADC to achieve envelope sampling. This allows the selection of an ADC with a higher quantization bit depth to improve the accuracy of envelope sampling, thereby improving the accuracy of detection.

[0049] In one possible implementation, the low-pass filter device 7 is a low-pass filter hardware circuit or an external low-pass filter. The low-pass filter device 7, being a low-pass filter hardware circuit or an external low-pass filter, can filter out high-frequency interference signals in advance; simultaneously, it eliminates the need for CPU involvement in filtering operations and does not consume system resources.

[0050] In one possible implementation, the low-pass filter 7 can be an active filter or a passive filter. Passive filters are simple in structure, low in cost, and highly reliable, and can operate without a power supply; active filters offer superior filtering performance, providing gain and strong load capacity. The choice between an active or passive low-pass filter 7 allows for flexible selection.

[0051] In one possible implementation, the low-pass filter 7 is an active filter, which can be an elliptic filter, a Butterworth filter, or a Chebyshev filter. The order of the filter is not limited and can be adjusted to suit different service scenarios.

[0052] Active filters can amplify signals through built-in operational amplifiers and other active devices, enhancing useful signals without the need for additional amplification modules, while effectively suppressing noise; and they have extremely low output impedance, making it easy to drive subsequent circuits and avoiding signal attenuation and distortion during transmission.

[0053] In one possible implementation, the low-pass filter 7 is a 5th-order Chebyshev filter. At the same order, a 5th-order Chebyshev filter has a steeper transition band than a Butterworth filter, allowing for a faster transition from the passband to the stopband; it is less sensitive to changes in component parameters and exhibits better stability; and compared to higher-order filters, it requires fewer components to meet filtering performance requirements, thus simplifying circuit design.

[0054] To enable those skilled in the art to better understand the optical signal conditioning device, the following specific embodiments will be used to further illustrate how the optical signal conditioning device regulates the optical signal.

[0055] Photomultiplier tubes convert the light signal of scattered light into a current signal;

[0056] The photocurrent signal is converted into a voltage signal using a transimpedance amplifier.

[0057] Since the laser repetition rate used is in the tens of MHz range, the secondary signal generates scattered light after passing through the test object, and the characteristics of the scattered light are consistent with those of the original laser. In this embodiment, a 5th-order Chebyshev filter is added to the hardware to preprocess the voltage signal, filtering out high-frequency signals and retaining only the effective low-frequency information. This reduces the specification requirements for the ADC to achieve envelope sampling, allowing for the selection of an ADC with a higher quantization bit depth to improve the accuracy of envelope sampling and thus enhance the detection accuracy. The ADC sampling circuit 2 digitizes the low-frequency signal, and the data is processed by an FPGA / CPU to obtain the wafer defect detection results.

[0058] When a wafer defect is identified, the gain of the photomultiplier tube can be adjusted by connecting the digital-to-analog converter module 4 and the high-voltage module 5, which are connected in sequence to the processor 3. This adjusts the scattered light signal, reduces overexposure of the scattered light, and improves the accuracy of wafer defect detection.

[0059] In the optical signal conditioning device provided in this embodiment, the photoelectric signal is preprocessed through the low-pass filter device 7. Compared with the direct sampling scheme of ADC, this avoids the interference of high-frequency noise on data sampling and data normalization processing. After passing through the low-pass filter device 7, the high-frequency components of the output signal of the photodetector 1 are filtered out, so that a low-specification ADC can be used to realize the digitization of analog signals, reducing hardware costs and analog circuit complexity. Moreover, the ADC sampling rate is reduced, which lowers the specification requirements for the ADC to realize envelope sampling. This allows the selection of an ADC with a higher quantization bit to improve the accuracy of envelope sampling, thereby improving the detection accuracy.

[0060] Example 3

[0061] The above embodiments describe an optical signal conditioning device. This embodiment also provides a wafer defect detection device, including: a laser source and the above-described optical signal conditioning device, wherein the laser source is used to emit laser light to irradiate the wafer.

[0062] The selection of the laser source is not limited and is determined based on the actual situation. The wafer defect detection device provided in this embodiment includes the optical signal conditioning device described above. The embodiments of the optical signal conditioning device have been described in detail above, and the embodiments of the wafer defect detection device will not be repeated here, and the effect is the same as above.

[0063] The above-described preferred embodiments have further detailed the purpose, technical solution, and advantages of this utility model. It should be understood that the above description is only a preferred embodiment of this utility model and is not intended to limit this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. An optical signal conditioning device, characterized in that, include: Photodetector, ADC sampling circuit, processor, digital-to-analog converter module, and high-voltage module; The first input terminal of the photodetector is used to receive the scattered light signal generated after the wafer is irradiated by a laser; the output terminal of the photodetector is connected to the input terminal of the ADC sampling circuit. The output of the ADC sampling circuit is connected to the input of the processor; the output of the processor is connected to the input of the digital-to-analog converter module. The output terminal of the digital-to-analog converter module is connected to the input terminal of the high-voltage module; the output terminal of the high-voltage module is connected to the second input terminal of the photodetector.

2. The optical signal conditioning device according to claim 1, characterized in that, Also includes: Current-to-voltage conversion module; The output terminal of the photodetector is connected to the input terminal of the ADC sampling circuit through the current-to-voltage conversion module.

3. The optical signal conditioning device according to claim 2, characterized in that, Also includes: Low-pass filter; The current-to-voltage conversion module is connected to the input terminal of the ADC sampling circuit through the low-pass filter.

4. The optical signal conditioning device according to claim 3, characterized in that, The low-pass filter device is a low-pass filter hardware circuit or an external low-pass filter.

5. The optical signal conditioning device according to claim 3, characterized in that, The low-pass filter device is either an active filter or a passive filter.

6. The optical signal conditioning device according to claim 5, characterized in that, The low-pass filter is an active filter, which is an elliptic filter, a Butterworth filter, or a Chebyshev filter.

7. The optical signal conditioning device according to claim 6, characterized in that, The low-pass filter is a 5th-order Chebyshev filter.

8. The optical signal conditioning device according to any one of claims 1 to 7, characterized in that, The photodetector is a photomultiplier tube.

9. The optical signal conditioning device according to any one of claims 2 to 7, characterized in that, The current-to-voltage conversion module is a transimpedance amplifier.

10. A wafer defect detection device, characterized in that, Includes: a laser source, and an optical signal conditioning device as described in any one of claims 1 to 9, wherein the laser source is used to emit laser light to irradiate the wafer.

Images