Method for detecting metal pollution of silicon wafer

Abstract

The invention relates to a method for detecting metal pollution of a silicon wafer, which belongs to the technical field of silicon wafer processing, and comprises the following operation steps of: 1, adopting infrared laser as an illumination light source for the silicon wafer, and enabling the illumination light source to be linear; and 2, moving the wafer under a linear strip line of an irradiation source to scan the whole silicon wafer. And 3, near-infrared excitation and light path design are carried out to detect and collect the thickness and PL signals of the whole silicon wafer. And 4, setting the scanning speed, the exposure time and the laser power to achieve synchronization of the laser and the detector. And 5, collecting light emitted after the whole surface of the silicon wafer is scanned by a detector in the form of a PL diagram. And 6, judging whether the silicon wafer is polluted by metal or not according to the luminous pattern collected by the detector. The method has the characteristics of convenient operation, high sensitivity and high identification accuracy. The method is used for evaluating the crystal quality of the whole wafer, and is applied to quality control of products in process or quality control of processing processes such as heat treatment.

Description

Technical Field

[0001] The present invention relates to the field of silicon wafer processing technology, and in particular to a method for detecting metal contamination of a silicon wafer. Background Art

[0002] It is well known that metal impurities in silicon crystals have a great negative effect on the performance of devices. In modern large-scale integrated circuit processes, the content of metal impurities is roughly controlled below 1013cm-3. Despite this, a small amount of metal impurities still affects the performance of silicon materials and devices. In a sub-micron integrated circuit, a tiny metal precipitate can damage its electrical properties and cause the failure of the entire integrated circuit. Therefore, controlling and reducing the pollution and harm of metal impurities in silicon is one of the keys to improving the production efficiency and device quality of modern large-scale integrated circuits.

[0003] Since metal impurities in silicon are often in the state of single atoms or precipitation, the measurement of metal impurities in silicon can be divided into three situations: one is to measure the overall concentration of various metal impurities in silicon, one is to measure the concentration of various metal single atoms in silicon, and the other is to measure the concentration of metal precipitation in silicon. Regardless of the state of metal impurities, they will reduce the minority carrier lifetime and minority carrier diffusion length of silicon materials and devices.

[0004] The SPV method can directly and quantitatively detect the Fe concentration on the surface and in the body of boron-doped P-type silicon single crystals. For P-type B-doped single crystal silicon, the dopant B can combine with Fe to form a FeB complex. If light with energy greater than the bandgap is introduced to break up the FeB complex and measure the minority carrier diffusion length before and after light exposure, the Fe concentration in the silicon crystal can be tested. However, the SPV method can only detect lightly B-doped single crystal silicon, and can only detect a limited number of elements, iron and copper.

[0005] Although fluorescence analyzers can be used for direct measurement, their detection sensitivity is relatively poor and they cannot completely detect trace amounts of metal contamination such as elemental metals or metal ions. Therefore, when using TXRF for measurement, it is necessary to cooperate with appropriate sampling techniques. For example, although ICP-MS has good sensitivity, it cannot be measured directly during ICP-MS measurement and requires chemical pre-treatment analysis steps, which can easily cause sample loss and contamination problems, and the pre-treatment steps are complicated and time-consuming. Summary of the invention

[0006] The present invention mainly solves the deficiencies in the prior art and provides a method for detecting metal contamination of silicon wafers, which has the characteristics of convenient operation, high sensitivity and high recognition accuracy. It is used to evaluate the crystal quality of the entire wafer, has high sensitivity, is an effective method for quickly identifying metal contaminated areas, and is applied to the quality control of in-process products or the quality control of processing processes such as heat treatment.

[0007] The above technical problems of the present invention are mainly solved by the following technical solutions: A method for detecting metal contamination of a silicon wafer comprises the following steps: Step 1: Use infrared laser as the illumination light source for the silicon wafer, and the illumination source is in a straight line.

[0008] Step 2: Scan the entire silicon wafer by moving the wafer under a linear line of irradiation source. This scanning method ensures that every area of ​​the silicon wafer can be irradiated by infrared laser, achieving full coverage detection and leaving out any part that may have metal contamination.

[0009] Step 3: Design of near-infrared excitation and optical path to detect and collect the entire silicon wafer thickness and PL signal.

[0010] Step 4: Set the scan speed, exposure time and laser power to achieve synchronization between the laser and the detector.

[0011] Step 5: The detector collects the light emitted after scanning the entire surface of the silicon wafer in the form of a PL map. The PL map can intuitively reflect the luminescence conditions at different locations on the surface and inside of the silicon wafer, providing rich image information for subsequent judgment of metal contamination.

[0012] Step 6: Determine whether the silicon wafer is contaminated by metal based on the luminescence image collected by the detector.

[0013] The detection and collection adopts the following technical solutions: (1) Detector selection: Select a near-infrared detector with high sensitivity and low noise. Use a detector based on mercury cadmium telluride (HgCdTe) material, which has excellent detection performance in the near-infrared band and can accurately capture the weak light signals emitted by silicon wafers under near-infrared excitation.

[0014] (2) Detection optical path design: Design a detection optical path that matches the excitation optical path to ensure that the detector can collect the optical signals emitted from all angles of the silicon wafer to the greatest extent possible. Use optical elements such as reflectors and condensers to guide scattered light and emitted light to the effective receiving area of ​​the detector to reduce the loss of optical signals. At the same time, set an aperture in the detection optical path to control the light flux entering the detector, avoid detector saturation, and ensure the linearity of the signal.

[0015] (3) Signal amplification and processing: A low-noise preamplifier and signal processing circuit are connected after the detector. The preamplifier can amplify the weak photocurrent signal while maintaining the signal-to-noise ratio. The signal processing circuit filters and digitizes the amplified signal for subsequent analysis and display.

[0016] Preferably, near-infrared excitation and optical path are further enhanced by diffusion of photogenerated carriers; near-infrared excitation and optical path effects are further enhanced by diffusion of photogenerated carriers, and diffusion of photogenerated carriers in silicon wafers is promoted by optimizing the electric field distribution and material structure inside the silicon wafer. The surface of the silicon wafer is specially doped to form a suitable electric field gradient, guiding the diffusion of photogenerated carriers in a specific direction, thereby enhancing the excitation effect.

[0017] Preferably, the photoluminescence imaging technology is used on the silicon wafer, the excitation wavelength is kept unchanged, and the emission wavelength is scanned, that is, the spectrum obtained by measuring the luminous flux or intensity as the wavelength of the emitted light changes, reflects the relative intensity of various wavelength components under the same excitation wavelength. Since different impurities correspond to different luminescent wavelengths, it is used to detect impurities and defects in silicon wafers.

[0018] High-quality near-infrared optical lenses and reflectors are used in the optical path. The lens should have the characteristics of low dispersion and high transmittance to ensure the quality of near-infrared light during transmission. The reflectivity of the reflector should be high, and its surface flatness should reach the nanometer level to reduce light loss and scattering. These optical components are reasonably arranged so that the optical path forms a stable near-infrared excitation channel, ensuring that the excitation light can accurately irradiate the silicon wafer and generate effective photoluminescence signals.

[0019] Preferably, a precise collimation and focusing system is used to keep the near-infrared light in a well-collimated state before reaching the silicon wafer; the direction of the light path and the focusing position are precisely controlled through an adjustable optical platform and a high-precision shifter to form a light spot with a suitable diameter and uniform energy distribution on the surface of the silicon wafer, thereby improving the excitation efficiency and detection sensitivity.

[0020] Preferably, an infrared laser with a wavelength of 808nm is selected as the illumination light source, and it is set as a linear illumination source. This wavelength of infrared laser can interact well with the silicon wafer, and the linear illumination source is conducive to subsequent scanning operations, and can provide stable and uniform illumination conditions, laying the foundation for comprehensive detection of the surface and internal conditions of the silicon wafer.

[0021] Preferably, set appropriate scanning speed, exposure time and laser power to achieve synchronization between the laser and the detector. The scanning speed should be determined according to the size of the silicon wafer and the detection accuracy requirements. Too fast a speed may lead to incomplete signal acquisition, while too slow a speed will reduce the detection efficiency. The exposure time should match the laser power and the photoluminescence characteristics of the silicon wafer to ensure that the detector can collect clear signals under the appropriate light intensity. The laser power setting should ensure that sufficient excitation energy is provided without damaging the silicon wafer, so that the silicon wafer can generate detectable photoluminescence signals. By precisely adjusting these parameters, perfect synchronization between laser excitation and detector signal acquisition can be achieved, improving the accuracy and stability of detection.

[0022] Preferably, the presence of metal contamination is determined based on the PL map. The intensity of the light emitted from the silicon wafer is proportional to the density of the unbalanced minority carriers at that location. The area where metal impurities are present in the silicon wafer will become a strong recombination center for minority carriers. Therefore, the minority carrier density in this area decreases, resulting in a weakened fluorescence effect. The area with lower PL brightness appears as dark dots, lines, circles or certain areas on the image compared to the brighter silicon wafer background. Through visual analysis of the PL map, it is preliminarily determined whether the silicon wafer has metal contamination and the approximate location of the contamination.

[0023] By measuring the photoluminescence images of silicon wafers in various states, it is used to monitor metal contamination on the surface and in the body of silicon wafers and metal contamination introduced during device manufacturing. It can qualitatively explain the existence of metal impurity contamination, but cannot quantitatively calculate the metal concentration in the silicon wafer. It can achieve high sensitivity in detecting metal contamination in silicon wafers, convenient detection, fast speed, and non-destructiveness, and can also be used for online monitoring.

[0024] Preferably, a method for quantitatively calculating the metal concentration in silicon wafers is adopted. A series of standard silicon wafer samples with known metal concentrations are first prepared, and the standard samples are tested to obtain the PL map and corresponding light signal intensity data of each sample; a calibration curve is drawn with the metal concentration as the horizontal axis and the light signal characteristic parameters of a specific area in the PL map as the vertical axis.

[0025] Preferably, the PL map of the silicon wafer to be tested is analyzed to extract the characteristic parameters of the light signal that are the same as those in the calibration curve; the total area of ​​the dark area in the PL map, the average brightness and other parameters are calculated by the image analysis algorithm based on the calibration curve and the light signal parameters of the silicon wafer to be tested. The metal concentration in the silicon wafer is calculated by interpolation or fitting equations. If the calibration curve is a linear relationship, the metal concentration can be solved by a simple linear equation; if it is a nonlinear relationship, a suitable nonlinear fitting method is used for calculation.

[0026] The present invention can achieve the following effects: The present invention provides a method for detecting metal contamination of silicon wafers, which is convenient to operate, highly sensitive and highly accurate in recognition compared with the prior art. By measuring the photoluminescence images of silicon wafers in various states, it is used to monitor the metal contamination on the surface and in the body of the silicon wafer and the metal contamination introduced during the device manufacturing process. It is used to evaluate the crystal quality of the entire wafer, has high sensitivity, and is an effective method for quickly identifying metal contamination areas. It is applied to the quality control of in-process products or the quality control of processing processes such as heat treatment. DETAILED DESCRIPTION

[0027] The technical solution of the invention is further specifically described below through embodiments.

[0028] Embodiment: A method for detecting metal contamination of a silicon wafer comprises the following steps: Step 1: Use infrared laser as the illumination source for the silicon wafer, and the illumination source is in a straight line. Select an infrared laser with a wavelength of 808nm as the illumination source, and set it as a straight line illumination source.

[0029] Step 2: Scan the entire silicon wafer by moving the wafer under a linear line of irradiation source.

[0030] Step 3: Design of near-infrared excitation and optical path to detect and collect the entire silicon wafer thickness and PL signal. The near-infrared excitation and optical path are further enhanced by the diffusion of photogenerated carriers. The diffusion of photogenerated carriers is used to further enhance the near-infrared excitation and optical path effects, and the diffusion of photogenerated carriers in the silicon wafer is promoted by optimizing the electric field distribution and material structure inside the silicon wafer.

[0031] A precise collimation and focusing system is used to keep the near-infrared light in a well-collimated state before reaching the silicon wafer; the direction of the light path and the focusing position are precisely controlled through an adjustable optical platform and a high-precision shifter to form a light spot with a suitable diameter and uniform energy distribution on the surface of the silicon wafer, thereby improving the excitation efficiency and detection sensitivity.

[0032] The detection and collection adopts the following technical solutions: (1) Detector selection: Select a near-infrared detector with high sensitivity and low noise. Use a detector based on mercury cadmium telluride (HgCdTe) material, which has excellent detection performance in the near-infrared band and can accurately capture the weak light signals emitted by silicon wafers under near-infrared excitation.

[0033] (2) Detection optical path design: Design a detection optical path that matches the excitation optical path to ensure that the detector can collect the optical signals emitted from all angles of the silicon wafer to the greatest extent possible. Use optical elements such as reflectors and condensers to guide scattered light and emitted light to the effective receiving area of ​​the detector to reduce the loss of optical signals. At the same time, set an aperture in the detection optical path to control the light flux entering the detector, avoid detector saturation, and ensure the linearity of the signal.

[0034] (3) Signal amplification and processing: A low-noise preamplifier and signal processing circuit are connected after the detector. The preamplifier can amplify the weak photocurrent signal while maintaining the signal-to-noise ratio. The signal processing circuit filters and digitizes the amplified signal for subsequent analysis and display.

[0035] Step 4: Set the scan speed, exposure time and laser power to achieve synchronization between the laser and the detector.

[0036] Set appropriate scanning speed, exposure time and laser power to achieve synchronization between the laser and the detector. The scanning speed should be determined according to the size of the silicon wafer and the detection accuracy requirements. Too fast a speed may lead to incomplete signal acquisition, while too slow a speed will reduce the detection efficiency; the exposure time should match the laser power and the photoluminescence characteristics of the silicon wafer to ensure that the detector can collect clear signals under the appropriate light intensity; the laser power setting should ensure that sufficient excitation energy is provided without damaging the silicon wafer, so that the silicon wafer produces a detectable photoluminescence signal.

[0037] Photoluminescence imaging technology is used on silicon wafers to keep the excitation wavelength unchanged and scan the emission wavelength. That is, the spectrum obtained by measuring the change of luminous flux or intensity with the wavelength of the emitted light reflects the relative intensity of various wavelength components under the same excitation wavelength.

[0038] Step 5: The detector collects the light emitted after scanning the entire surface of the silicon wafer in the form of a PL image.

[0039] Step 6: Determine whether the silicon wafer is contaminated by metal based on the luminescence image collected by the detector.

[0040] The presence of metal contamination can be determined based on the PL graph. The intensity of the photoluminescence light emitted from the silicon wafer is proportional to the density of the unbalanced minority carriers at that location. The areas where metal impurities are contaminated in the silicon wafer will become strong recombination centers of minority carriers. Therefore, the minority carrier density in this area decreases, resulting in a weakened fluorescence effect. Areas with lower PL brightness appear as dark dots, lines, circles or certain areas on the image compared to the brighter silicon wafer background.

[0041] The method of quantitatively calculating the metal concentration in silicon wafers is adopted. A series of standard silicon wafer samples with known metal concentrations are first prepared. The standard samples are tested to obtain the PL map and corresponding light signal intensity data of each sample. The calibration curve is drawn with the metal concentration as the horizontal axis and the light signal characteristic parameters of a specific area in the PL map as the vertical axis. The PL map of the silicon wafer to be tested is analyzed to extract the light signal characteristic parameters that are the same as those in the calibration curve. According to the calibration curve and the light signal parameters of the silicon wafer to be tested, the metal concentration in the silicon wafer is calculated using the interpolation method or fitting equation.

[0042] In summary, the detection method of metal contamination of silicon wafers is characterized by convenient operation, high sensitivity and high recognition accuracy. By measuring the photoluminescence images of silicon wafers in various states, it is used to monitor the metal contamination on the surface and in the body of the silicon wafer and the metal contamination introduced during the device manufacturing process. It is used to evaluate the crystal quality of the entire wafer, has high sensitivity, and is an effective method for quickly identifying metal contamination areas. It is used for quality control of in-process products or quality control of processing processes such as heat treatment.

[0043] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A method for detecting metal contamination of a silicon wafer, characterized in that The steps are as follows: Step 1: Use infrared laser as the illumination light source for the silicon wafer, and the illumination source is in a straight line; Step 2: Scan the entire silicon wafer by moving the wafer along a straight line of irradiation source; Step 3: Design of near-infrared excitation and optical path to detect and collect the entire silicon wafer thickness and PL signal; Step 4: Set the scan speed, exposure time and laser power to achieve synchronization between the laser and the detector; Step 5: The detector collects the light emitted after scanning the entire surface of the silicon wafer in the form of a PL map; Step 6: Determine whether the silicon wafer is contaminated by metal based on the luminescence image collected by the detector.

2. The method for detecting metal contamination of a silicon wafer according to claim 1, characterized in that: The near-infrared excitation and optical path are further enhanced by the diffusion of photogenerated carriers; the diffusion of photogenerated carriers is utilized to further enhance the near-infrared excitation and optical path effects, and the diffusion of photogenerated carriers in the silicon wafer is promoted by optimizing the electric field distribution and material structure inside the silicon wafer.

3. The method for detecting metal contamination of a silicon wafer according to claim 2, characterized in that: Photoluminescence imaging technology is used on silicon wafers to keep the excitation wavelength unchanged and scan the emission wavelength. That is, the spectrum obtained by measuring the change of luminous flux or intensity with the wavelength of the emitted light reflects the relative intensity of various wavelength components under the same excitation wavelength.

4. The method for detecting metal contamination of silicon wafer according to claim 3, characterized in that: A precise collimation and focusing system is used to keep the near-infrared light in a well-collimated state before reaching the silicon wafer; the direction of the light path and the focusing position are precisely controlled through an adjustable optical platform and a high-precision shifter to form a light spot with a suitable diameter and uniform energy distribution on the surface of the silicon wafer, thereby improving the excitation efficiency and detection sensitivity.

5. The method for detecting metal contamination of silicon wafer according to claim 1, characterized in that: An infrared laser with a wavelength of 808 nm is selected as the illumination light source, and is set as a linear illumination source.

6. The method for detecting metal contamination of silicon wafer according to claim 1, characterized in that: Set appropriate scanning speed, exposure time and laser power to achieve synchronization between the laser and the detector; the scanning speed should be determined according to the size of the silicon wafer and the detection accuracy requirements. Too fast a speed may lead to incomplete signal acquisition, while too slow a speed will reduce the detection efficiency; the exposure time should match the laser power and the photoluminescence characteristics of the silicon wafer to ensure that the detector can collect clear signals under appropriate light intensity; the laser power should be set to ensure that sufficient excitation energy is provided without damaging the silicon wafer, so that the silicon wafer produces a detectable photoluminescence signal.

7. The method for detecting metal contamination of silicon wafer according to claim 1, characterized in that: The presence of metal contamination can be determined based on the PL graph. The intensity of the photoluminescence light emitted from the silicon wafer is proportional to the density of the unbalanced minority carriers at that location. The areas where metal impurities are contaminated in the silicon wafer will become strong recombination centers of minority carriers. Therefore, the minority carrier density in this area decreases, resulting in a weakened fluorescence effect. Areas with lower PL brightness appear as dark dots, lines, circles or certain areas on the image compared to the brighter silicon wafer background.

8. The method for detecting metal contamination of silicon wafer according to claim 1, characterized in that: A method for quantitatively calculating the metal concentration in silicon wafers is adopted. First, a series of standard silicon wafer samples with known metal concentrations are prepared. The standard samples are tested to obtain the PL map and corresponding light signal intensity data of each sample. A calibration curve is drawn with the metal concentration as the horizontal axis and the light signal characteristic parameters of a specific area in the PL map as the vertical axis.

9. The method for detecting metal contamination of a silicon wafer according to claim 8, characterized in that: The PL image of the silicon wafer to be tested is analyzed to extract the characteristic parameters of the optical signal that are the same as those in the calibration curve; based on the calibration curve and the optical signal parameters of the silicon wafer to be tested, the metal concentration in the silicon wafer is calculated using the interpolation method or the fitting equation.