Method for producing field oxide layer of silicon carbide chip

Abstract

The application discloses a field oxidation layer preparation method of silicon carbide chip, and particularly relates to the technical field of silicon carbide chip preparation, and comprises the following steps: S1, preliminary treatment; S2, detection and identification; S3, wafer treatment; S4, double correction; S5, removal operation; S6, wafer detection; S7, cleaning and annealing; and S8, final detection, wherein the polarization state change of light after reflection on the surface of the silicon oxide film is measured. The high-resolution image acquisition CCD camera is used to shoot the pattern after the film hardening, clear images are acquired, and the light is sufficient during the image acquisition process, including noise removal, contrast enhancement, edge detection, key features, such as line width, spacing and shape, are extracted from the pretreated images, whether there is deviation or defect is checked, and when the comparison and analysis are performed, the automatic comparison algorithm can be adopted to realize automatic detection of whether each step of preparation is qualified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductors, and more particularly, to a method for preparing a field oxide layer of a silicon carbide chip. BACKGROUND

[0002] Silicon carbide is an advanced third-generation semiconductor material with high frequency, high efficiency, and high power. It not only meets the needs of national major strategies such as intelligent manufacturing, energy saving and emission reduction, and information security, but also supports the development of key electronic components for mobile communication and energy internet. In order to improve the breakdown voltage of a silicon carbide chip in a static off state, a field oxide layer needs to be formed on a silicon carbide epitaxial layer. Defects in the field oxide can easily cause field tube leakage, losing the isolation function and making the die lose its function.

[0003] After searching the existing published technical documents, a high-voltage silicon carbide device and a preparation method are disclosed in Chinese patent No. CN117542734A. The preparation technology increases the P region injection junction depth by etching a groove at the edge of the chip, so that the equipotential surface of the back electrode is not on the scribe line surface during reverse voltage testing. When the deep PN junction formed by etching is reverse depleted, its electric field gradient is almost entirely transferred to the depletion region, and the potential on the scribe line surface will be greatly reduced. The potential difference between the two is not enough to excite air ionization, thereby avoiding the occurrence of sparking phenomenon. Moreover, the PN junction formed after etching is deeper, and the electric field gradient is transferred to a deeper epitaxial layer, so the terminal to the scribe line can be designed to be smaller, thereby improving wafer utilization and reducing costs. However, the preparation method has the following defects:

[0004] The preparation method can achieve preparation of the field oxide layer of the silicon carbide chip, but it is difficult to achieve precise control at each step during the preparation process, which results in poor control accuracy and makes it difficult to achieve precise preparation. SUMMARY

[0005] To overcome the above-mentioned defects of the prior art, the present application provides a method for preparing a field oxide layer of a silicon carbide chip.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a method for preparing a field oxide layer of a silicon carbide chip, comprising the following specific steps:

[0007] S1, preliminary treatment, spin coating photoresist on the silicon oxide medium layer, exposing after baking at 120-150℃ for 120-150s; then baking at 120-150℃ for 60-80s, and then developing and hardening the film;

[0008] S2, detection and identification, use high-resolution image acquisition CCD camera to take pictures of the image after the film, if there is deviation or defect, need to return to work according to the specific situation;

[0009] S3, wafer processing, wafer in oxygen, nitrogen and vacuum protection environment, 20 seconds of scanning glue, to ensure that the photoresist is not left in the photoresist development area;

[0010] S4, double check, high-resolution image acquisition device to scan the wafer coated with photoresist to get clear image, image analysis algorithm double detection, according to the results of double detection, to determine whether the wafer is qualified;

[0011] S5, removal operation, using dry etching process to etch 700-900nm thickness of silicon oxide, in BOE solution for 100-120s to etch the remaining thickness of silicon oxide;

[0012] S6, wafer detection, using high-resolution optical microscope to observe the wafer surface 5-10 times, comparing the images before and after etching, checking whether the silicon oxide layer is completely removed, observing the surface morphology of the silicon oxide layer, and judging whether there is residual;

[0013] S7, cleaning and annealing, after field oxygen etching, wafer needs to be treated and annealed;

[0014] S8, final detection, by measuring the polarization state change of light reflected on the surface of silicon oxide thin film, accurately measuring the thickness of the thin film, and checking whether it is within the design range.

[0015] Preferably, the S1 hard film process forms a more firm chemical bond and physical connection between the photoresist and the substrate by heating.

[0016] Preferably, the S2 takes 5-10 pictures to get clear image, the light is sufficient and the focus is accurate during image acquisition process, to reduce image blur and distortion, the collected image is preprocessed, including denoising, contrast enhancement and edge detection, the key features, line width, spacing and shape, are extracted from the preprocessed image, these features should be consistent with the design requirements, the extracted features are compared with the design drawing or standard template, to check whether there is deviation or defect, during comparison and analysis, automatic comparison algorithm can be used, according to the comparison and analysis results, to determine whether the photoresist pattern is qualified.

[0017] Preferably, the S4 is pre-processed and feature extraction 5-10 times by image processing software to identify the pattern on the wafer and the coating image of the photoresist, and the preset qualified standard is 5-10 mm, the line width, the pitch, the photoresist thickness, the extracted features are compared and analyzed, and the obviously unqualified wafer is quickly screened out, and the wafer close to the critical value in the first detection is 0.5-2 mm.

[0018] Preferably, the S6 is measured by an ellipsometer by measuring the polarization state change of light reflected on the sample surface to 50-80 nm, so as to accurately determine the thickness of the film, and after etching and BOE etching, the ellipsometer is used to measure the silicon oxide layer on the wafer, and the difference value range of the thickness data before etching is 50-60 nm, so as to judge whether the remaining thickness is zero or close to zero.

[0019] Preferably, the S7 is that the wafer surface needs to be strictly cleaned and pretreated to remove residual photoresist, contaminants and impurities. The wafer is placed in an annealing furnace and heat treated at a temperature of 800 to 1300 DEG C, while ensuring that the whole process is carried out in a nitrogen atmosphere or a vacuum environment, and the heat preservation time is maintained between 0.5 to 2 h.

[0020] Preferably, the S8 is that X-ray diffraction is used to analyze the crystal structure and phase composition of the silicon oxide film, high-resolution optical microscopy is used to observe the surface morphology of the silicon oxide film, and four-probe testing is used to measure the resistivity of the silicon oxide film 5-10 times.

[0021] The S8 is that the optical microscope focuses laser on the wafer, illuminates a light spot, and the reflected light is refocused on the receiving plane, and the wafer surface is detected by analyzing the light. The resolution of the optical microscope is limited, but it plays an important role in detecting particles and defects on the wafer surface. The S8 is that the film thickness is measured by a small spectrometer controlled by an embedded microprocessor. The light emitted by the light source becomes elliptical polarized light after collimation and polarization. After refraction and reflection on the sample surface, the polarization state of the light changes. By alternately changing the polarizer and the analyzer, the reflected light becomes linearly polarized light, and the extinction information is obtained after the extinction of the analyzer. The thickness of the film is calculated.

[0022] The technical effects and advantages of the present application are as follows:

[0023] 1、The present application uses high-resolution image acquisition CCD camera to shoot the pattern after the film, and clear images are obtained, the light is sufficient and the focus is accurate during the image acquisition process, so as to reduce image blur and distortion, the collected images are preprocessed, including denoising, contrast enhancement and edge detection, key features such as line width, spacing and shape are extracted from the preprocessed images, these features should be consistent with the design requirements, and whether there is deviation or defect is checked, when comparison and analysis, automatic comparison algorithm can be used to realize automatic detection of whether each step of preparation is qualified, and the preparation accuracy is improved.

[0024] 2、The present application scans the wafer coated with photoresist through high-resolution image acquisition equipment, line width, spacing and photoresist thickness, and compares and analyzes the extracted features, so as to quickly screen out obviously unqualified wafers, obtain clear images, and realize high-precision preparation treatment through double detection of image analysis algorithm, comparison of images before and after etching, and checking whether the silicon oxide layer is completely removed or not, and judging whether the remaining thickness is zero or close to zero by measuring the polarization state change of light reflected on the sample surface through an ellipsometer.

[0025] 3、The present application uses the polarization state change of the measurement light reflected on the surface of the silicon oxide thin film, X-ray diffraction for analyzing the crystal structure and phase composition of the silicon oxide thin film, high-resolution optical microscope for observing the surface morphology of the silicon oxide thin film, whether there are cracks and pinhole defects, and four-probe test for checking whether the resistivity of the silicon oxide thin film is within the design range. DETAILED DESCRIPTION

[0026] Figure 1 The present application is a method for preparing a field oxide layer of a silicon carbide chip. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0028] As shown in the accompanying drawings of the embodiments of the present application, the following three groups of embodiments are obtained by the method for preparing a field oxide layer of a silicon carbide chip. Figure 1

[0029] Embodiment 1:

[0030] ​S1, preliminary processing, spin coating photoresist on the silicon oxide medium layer, after baking at 120°C for 120s, exposure; then baking at 120°C for 60s, development, hardening, the hardening process forms a more firm chemical bond and physical connection between the photoresist and the substrate by heating;

[0031] S2, detection and identification, use high-resolution image acquisition CCD camera to shoot the pattern after hardening, shoot 5 times to obtain clear images, sufficient light and accurate focusing during image acquisition to reduce image blur and distortion, pre-process the collected images, including denoising, contrast enhancement, edge detection, extract key features from the pre-processed images, line width, spacing, shape, these features should be consistent with the design requirements, compare and analyze the extracted features with the design drawing or standard template to check whether there is deviation or defect, when comparing and analyzing, automatic comparison algorithm can be used, according to the comparison and analysis result, determine whether the photoresist pattern is qualified, if there is deviation or defect, rework according to specific circumstances;

[0032] S3, wafer processing, the wafer is processed in the protection environment of oxygen, nitrogen and vacuum for 20 seconds to ensure that there is no photoresist residue in the photoetching development area;

[0033] S4, double check, high-resolution image acquisition equipment scans the wafer coated with photoresist, uses image processing software to pre-process and extract features 5 times to identify the pattern on the wafer and the coating image of the photoresist, the preset qualified standard is 5mm, line width, spacing, photoresist thickness, compare and analyze the extracted features, the detection aims to quickly screen out obviously unqualified wafers, for the wafer with fuzzy area or close to the critical value in the first detection, the clear image is obtained, the image analysis algorithm double checks, according to the double detection result, determine whether the wafer is qualified;

[0034] S5, removal operation, dry etching process is used to etch 700nm thick silicon oxide, image processing software is used to pre-process and extract features 5 times to identify the pattern on the wafer and the coating image of the photoresist, the preset qualified standard is 5mm, line width, spacing, photoresist thickness, compare and analyze the extracted features, the detection aims to quickly screen out obviously unqualified wafers, for the wafer with fuzzy area or close to the critical value in the first detection, the clear image is obtained, the image analysis algorithm double checks, according to the double detection result, determine whether the wafer is qualified;

[0035] S6, wafer detection, use high-resolution optical microscope to observe the wafer surface 5 times, compare the images before and after etching, check whether the silicon oxide layer is completely removed, measure the change of polarization state of light reflected on the sample surface by ellipsometer to 50 nm, to accurately determine the thickness of the film, after etching and BOE etching, use ellipsometer to measure the silicon oxide layer on the wafer, compare the thickness data before etching, the difference range is 50 nm, to judge whether the residual thickness is zero or close to zero;

[0036] S7, cleaning and annealing, after field oxygen etching is completed, the wafer surface needs to be cleaned and pretreated strictly to remove residual photoresist, contaminants and impurities, the wafer is placed in the annealing furnace, and heat preservation treatment is carried out at a temperature range of 800 DEG C, while ensuring that the whole process is carried out in a nitrogen protection or vacuum environment, and the heat preservation maintains 0.5 h;

[0037] S8, final detection, by measuring the change of polarization state of light reflected on the surface of silicon oxide film, X-ray diffraction is used to analyze the crystal structure and phase composition of the silicon oxide film, high-resolution optical microscope is used to observe the surface morphology of the silicon oxide film, to check whether there are cracks, pinhole defects, four-probe test, measure the resistivity of the silicon oxide film 5 times, accurately determine the thickness of the film, and check whether it is within the design range.

[0038] Example 2:

[0039] S1, preliminary treatment, spin coating photoresist on the silicon oxide medium layer, exposing after baking at 130 DEG C for 130 s; then baking at 130 DEG C for 50 s, then developing, hardening, the hardening process forms a more firm chemical bond and physical connection between the photoresist and the substrate by heating;

[0040] S2, detection and identification, use high-resolution image acquisition CCD camera to shoot the pattern after hardening, shoot 8 times to obtain clear images, sufficient light and accurate focusing during image acquisition to reduce image blur and distortion, pre-process the collected images, including denoising, contrast enhancement and edge detection, extract key features from the pre-processed images, line width, spacing and shape, these features should be consistent with the design requirements, compare and analyze the extracted features with the design drawing or standard template to check whether there is deviation or defect, when comparing and analyzing, automatic comparison algorithm can be used, according to the comparison and analysis result, determine whether the photoresist pattern is qualified, if there is deviation or defect, rework according to the specific situation;

[0041] S3, wafer treatment, the wafer is placed in the protection environment of oxygen, nitrogen and vacuum, and the photoresist is scanned for 20 seconds to ensure that there is no photoresist residue in the photoresist developing area;

[0042] S4, double-time calibration, high-resolution image acquisition device scans the wafer coated with photoresist, and image processing software is used to pre-process and extract features 8 times to identify the patterns on the wafer and the coating image of the photoresist, the preset qualified standard is 8mm, line width, spacing, photoresist thickness, the extracted features are compared and analyzed, the detection aims to quickly screen out obviously unqualified wafers, the wafer with a fuzzy area or close to the critical value in the first detection is 1mm, a clear image is obtained, the image analysis algorithm double-time detection, according to the results of double-time detection, it is determined whether the wafer is qualified;

[0043] S5, removal operation, dry etching process is used to etch the silicon oxide with a thickness of about 800m, image processing software is used to pre-process and extract features 8 times to identify the patterns on the wafer and the coating image of the photoresist, the preset qualified standard is 8mm, line width, spacing, photoresist thickness, the extracted features are compared and analyzed, the detection aims to quickly screen out obviously unqualified wafers, the wafer with a fuzzy area or close to the critical value in the first detection is 0.6mm, the wafer is soaked in BOE solution for 110s to corrode the remaining thickness of the silicon oxide;

[0044] S6, wafer detection, high-resolution optical microscope is used to observe the wafer surface 8 times, the images before and after etching are compared, the silicon oxide layer is checked whether it is completely removed, the thickness of the thin film is accurately determined by measuring the change of the polarization state of the light reflected on the sample surface to 70nm by ellipsometer, after etching and BOE corrosion, the silicon oxide layer on the wafer is measured by ellipsometer, the difference range of the thickness data before etching is compared to 55nm, whether the remaining thickness is zero or close to zero is judged;

[0045] S7, cleaning and annealing, after the field oxygen etching is completed, the wafer surface needs to be strictly cleaned and pretreated to remove the residual photoresist, contaminants and impurities, the wafer is placed in the annealing furnace for heat preservation treatment at a temperature range of 1000℃, and at the same time, it is ensured that the whole process is carried out in a nitrogen protection or vacuum environment, and the heat preservation maintains for 1h;

[0046] S8, final detection, by measuring the change of the polarization state of the light reflected on the surface of the silicon oxide thin film, X-ray diffraction is used to analyze the crystal structure and phase composition of the silicon oxide thin film, high-resolution optical microscope is used to observe the surface morphology of the silicon oxide thin film, whether there are cracks, pinhole defects, four-probe test is used to measure the resistivity of the silicon oxide thin film 8 times, the thickness of the thin film is accurately determined, and whether it is within the design range is viewed.

[0047] Example 3:

[0048] S1, preliminary processing, spin coating photoresist on the silicon oxide medium layer, after baking at 150°C for 150s, exposure; then baking at 150°C for 80s, developing, hardening, the hardening process forms a more firm chemical bond and physical connection between the photoresist and the substrate through heating;

[0049] S2, detection and identification, use high-resolution image acquisition CCD camera to shoot the pattern after hardening, shoot 10 times to obtain clear images, sufficient light and accurate focusing during image acquisition to reduce image blur and distortion, pre-process the collected images, including denoising, contrast enhancement, edge detection, extract key features from the pre-processed images, line width, spacing, shape, these features should be consistent with the design requirements, compare and analyze the extracted features with the design drawing or standard template to check whether there is deviation or defect, when comparing and analyzing, automatic comparison algorithm can be used, according to the comparison and analysis result, determine whether the photoresist pattern is qualified, if there is deviation or defect, rework according to specific circumstances;

[0050] S3, wafer processing, the wafer is processed in the protection environment of oxygen, nitrogen and vacuum for 20s to ensure that there is no photoresist residue in the photoetching development area;

[0051] S4, double check, high-resolution image acquisition equipment scans the wafer coated with photoresist, pre-processes and extracts features from the image 10 times to identify the pattern on the wafer and the coating image of the photoresist, the preset qualified standard is 10mm, line width, spacing, photoresist thickness, compare and analyze the extracted features, the detection aims to quickly screen out obviously unqualified wafers, for the first detection, the wafer with fuzzy area or close to the critical value is 2mm, clear images are obtained, image analysis algorithm double detection, according to the double detection result, determine whether the wafer is qualified;

[0052] S5, removal operation, dry etching process is used to etch 900nm thick silicon oxide, image processing software is used to pre-process and extract features from the image 10 times to identify the pattern on the wafer and the coating image of the photoresist, the preset qualified standard is 10mm, line width, spacing, photoresist thickness, compare and analyze the extracted features, the detection aims to quickly screen out obviously unqualified wafers, for the first detection, the wafer with fuzzy area or close to the critical value is 2mm, immerse in BOE solution for 120s to etch away the remaining thickness of silicon oxide;

[0053] S6, wafer detection, using high-resolution optical microscope to observe the wafer surface 10 times, comparing the images before and after etching, checking whether the silicon oxide layer is completely removed, measuring the change of the polarization state of the light reflected on the sample surface by ellipsometer to 80nm, to accurately determine the thickness of the film, after etching and BOE etching, using ellipsometer to measure the silicon oxide layer on the wafer, comparing the thickness data before etching, the difference range is 60nm, to judge whether the remaining thickness is zero or close to zero;

[0054] S7, cleaning and annealing, after the field oxygen etching is completed, the wafer surface needs to be cleaned and pretreated strictly to remove the residual photoresist, contaminants and impurities, the wafer is placed in the annealing furnace, and the heat preservation treatment is carried out at a temperature range of 1200 DEG C, while ensuring that the whole process is carried out in a nitrogen protection or vacuum environment, and the heat preservation is maintained for 2h;

[0055] S8, final detection, by measuring the change of the polarization state of the light reflected on the surface of the silicon oxide film, DX ray diffraction is used for analyzing the crystal structure and phase composition of the silicon oxide film, high-resolution optical microscope is used for observing the surface morphology of the silicon oxide film, checking whether there are cracks, pinhole defects, four-probe test, measuring the resistivity of the silicon oxide film 10 times, accurately determining the thickness of the film, and checking whether it is within the design range.

[0056] Manufacturing yield Precision lift rate Manufacturing damage rate Example 1 98.5 26.5 0.5 Example 2 99.6 27.6 0.35 Example 3 99.7 28.9 0.25

[0057] It can be known from the above table that the preparation qualified rate in example 3 is higher than that in example 2 and example 1, wherein the accurate improvement rate in example 3 is obviously higher than that in example 2 and example 1, and the preparation damage rate is obviously lower than that in example 2 and example 1. In summary, in the preparation process, whether each step of preparation is qualified is detected automatically, and the preparation accuracy is improved.

[0058] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for field oxidation layer preparation of silicon carbide chips, characterized by: The specific steps include: S1, preliminary treatment, spin coating photoresist on the silicon oxide medium layer, baking at 120-150 DEG C for 120-150 s, then exposing; again baking at 120-150 DEG C for 60-80 s, then developing, hardening film; S2, detection and identification, using high-resolution image acquisition CCD camera to shoot the image after hardening film, if there is deviation or defect, need to return to work according to the specific situation; S3, wafer processing, wafer in the protection environment of oxygen, nitrogen and vacuum, sweep glue 20 seconds, ensure that the photoresist is not left in the photoetching and developing area; S4, double correction, high-resolution image acquisition equipment scans the wafer coated with photoresist to obtain clear image, image analysis algorithm double detection, according to the result of double detection, determine whether the wafer is qualified; S5, removal operation, using dry etching process to etch the silicon oxide with a thickness of about 700-900 nm, soaking in BOE solution for 100-120 s to corrode the remaining thickness of silicon oxide; S6, wafer detection, using high-resolution optical microscope to observe the wafer surface 5-10 times, comparing the images before and after etching, checking whether the silicon oxide layer is completely removed, observing the surface morphology of the silicon oxide layer, judging whether there is residual; S7, cleaning and annealing, after field oxygen etching, the wafer needs to be treated and annealed; S8, final detection, by measuring the polarization state change of light reflected on the surface of the silicon oxide film, accurately measuring the thickness of the film, checking whether it is within the design range; In S2, 5-10 clear images are taken, the light is sufficient and the focus is accurate during image acquisition to reduce image blur and distortion, the collected images are preprocessed, including denoising, contrast enhancement and edge detection, key features such as line width, spacing and shape are extracted from the preprocessed images, these features should be consistent with the design requirements, the extracted features are compared and analyzed with the design drawing or standard template to check whether there is deviation or defect, during comparison and analysis, automatic comparison algorithm can be used, according to the comparison and analysis result, determine whether the photoresist pattern is qualified.

2. The method of claim 1, wherein: In S1, the hardening film process forms a more firm chemical bond and physical connection between the photoresist and the substrate by heating.

3. The method of claim 1, wherein: In S4, the image is preprocessed and feature extracted 5-10 times by image processing software to identify the pattern on the wafer and the coating image of the photoresist, the preset qualified standard is 5-10 mm, line width, spacing and photoresist thickness, the extracted features are compared and analyzed, the detection aims to quickly screen out obviously unqualified wafers, the wafer with fuzzy area or close to the critical value in the first detection is 0.5-2 mm.

4. The method of claim 1, wherein: In S6, the thickness of the film is accurately measured by measuring the polarization state change of light reflected on the sample surface by 50-80 nm, after etching and BOE corrosion, the ellipsometer is used to measure the silicon oxide layer on the wafer, the thickness data difference before etching is compared, the difference is 50-60 nm, to determine whether the remaining thickness is zero or close to zero.

5. The method of claim 1, wherein: The wafer surface in S7 needs to be cleaned and pretreated to remove residual photoresist, contaminants and impurities. The wafer is placed in an annealing furnace and treated at a temperature of 800-1300℃ for 0.5-2h in a nitrogen atmosphere or vacuum environment.

6. The method of claim 1, wherein: In S8, X-ray diffraction is used to analyze the crystal structure and phase composition of the silicon oxide film. High-resolution optical microscopy is used to observe the surface morphology of the silicon oxide film and check for cracks and pinhole defects. Four-probe testing is used to measure the resistivity of the silicon oxide film 5-10 times.

7. The method for preparing the field oxide layer of a silicon carbide chip according to claim 1, characterized in that: In S8, the optical microscope focuses laser light on the wafer to illuminate a spot. The reflected light is refocused on a receiving plane. By analyzing the light, the wafer surface can be detected.

8. The method for preparing the field oxide layer of a silicon carbide chip according to claim 1, characterized in that: In S8, a small spectrometer controlled by an embedded microprocessor is used to measure the film thickness. The light emitted by the light source is collimated and polarized into elliptical polarized light. After refraction and reflection on the sample surface, the polarization state of the light changes. By alternately changing the polarizer and analyzer, the reflected light becomes linearly polarized light, and after passing through the analyzer, the extinction information is obtained. The thickness of the film is calculated.

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