Film thickness quality assessment method for silicon carbide substrates

Abstract

A method for evaluating the film thickness quality of a silicon carbide substrate, belonging to the field of semiconductor technology, comprises the following steps: S1: selecting a silicon carbide substrate and growing a film layer on the silicon carbide substrate; S2: selecting several measurement angles and wavelength ranges, measuring phase change and amplitude attenuation using a spectroscopic ellipsometer, and obtaining the minimum MSE value based on the evaluation function MSE formula; S3: selecting several measurement positions, and obtaining the film thickness di and the evaluation function MSEi at the several positions based on the measurement angles and wavelength ranges corresponding to the minimum MSE value; S4: obtaining a weight coefficient Wi based on the evaluation function MSEi; S5: calculating and obtaining the film thickness mean and film thickness uniformity according to the formula. The present invention calculates the film thickness mean and film thickness uniformity using the evaluation function and weight coefficient, accurately and objectively reflecting the film thickness quality on the silicon carbide substrate.

Description

Technical Field

[0001] The invention belongs to the field of semiconductors, and in particular relates to a method for evaluating the film thickness quality of a silicon carbide substrate. Background Art

[0002] Silicon carbide, a third-generation semiconductor material, boasts a high critical breakdown electric field, high thermal conductivity, and high saturated electron drift velocity, making it superior to silicon in high-temperature, high-voltage, and high-frequency applications. In the fields of power electronics, radio frequency devices, and optoelectronics, MOSFETs and HEMTs based on silicon carbide are gaining increasing research.

[0003] Semiconductor processing primarily involves forming a patterned stack of different layers on epitaxial wafers through techniques such as photolithography, etching, thin film deposition, and interface oxidation. This is ultimately followed by scribing, chip testing, and packaging to produce usable chips. Different processing techniques in thin film and interface oxidation processes result in different coatings, such as PVD sputtering of carbon and metal films, CVD growth of silicon oxide and polysilicon films, and high-temperature oxidation for the production of nanostructured and silicon oxide films. Film thickness gauges and ellipsometers are commonly used to measure these various film layers. Film thickness gauges are primarily used for measuring translucent and opaque film layers, while ellipsometers are primarily used for thin transparent and translucent film layers.

[0004] Ellipsometers are categorized into laser ellipsometers and spectroscopic ellipsometers based on the type of light source they generate. Laser ellipsometers, due to their single light source, are only suitable for measuring fixed film layers in large-scale industrial production, and suffer from low measurement accuracy. Spectroscopic ellipsometers, covering long-wavelength light sources from ultraviolet and visible light to infrared, ensure a comprehensive range of film spectra can be measured with high accuracy, making them ideal for technology research and development.

[0005] Ellipsometer film thickness measurement on silicon substrates has been effectively verified. Due to the anisotropy of silicon carbide materials and the coating defects caused by different processing technologies, the research on ellipsometer film thickness measurement on silicon carbide substrates and epitaxy is still deepening. In the traditional spectroscopic ellipsometer measurement process, the data obtained by only single-position measurement cannot fully and objectively reflect the film thickness properties. Multiple measurements require manual selection of different positions and recalibration each time, which is time-consuming. This method combines the single-point single measurement mode of the ellipsometer with the multi-point single measurement mode, using the film thickness mean and uniformity as optimization indicators. The optimized film thickness mean and uniformity are used to represent the coating quality on the silicon carbide substrate, reflecting the film thickness properties on the silicon carbide substrate more accurately and objectively.

[0006] Due to the anisotropic effects of silicon carbide, variations in thickness, crystal orientation, and inherent defects such as micropipes and radiata between silicon carbide substrates or epitaxial wafers provided by different manufacturers can lead to significant deviations in the measured film thickness on silicon carbide substrates. Furthermore, this method, which measures film thickness through multiple measurements at a single point, cannot reflect the uniformity of the film thickness across the silicon carbide substrate. Summary of the Invention

[0007] The present invention aims to provide a method for evaluating the film thickness quality of a silicon carbide substrate, so as to solve the technical problem of evaluating the film thickness quality of a silicon carbide substrate.

[0008] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0009] A method for evaluating film thickness quality of a silicon carbide substrate comprises the following steps:

[0010] S1: selecting a silicon carbide substrate and growing a film layer on the silicon carbide substrate;

[0011] S2: Select several measurement angles and wavelength ranges and use spectroscopic ellipsometer to measure the phase change Δ and amplitude attenuation According to the evaluation function MSE formula, the minimum MSE value is obtained;

[0012] S3: Select several measurement positions, and obtain the film thickness di and evaluation function MSEi at the several positions according to the measurement angle and wavelength range corresponding to the minimum MSE value;

[0013] S4: Based on the evaluation function MSEi, a weight coefficient Wi is obtained;

[0014] S5: Calculate and obtain the film thickness mean and film thickness uniformity according to the formula.

[0015] Furthermore, the silicon carbide substrate includes a silicon carbide substrate sheet and a silicon carbide epitaxial wafer.

[0016] Furthermore, the film layer is at least one layer.

[0017] Furthermore, the step S2 includes the following steps:

[0018] S201: Select several measurement angles and wavelength ranges, use the single-point single-shot measurement method of the spectroscopic ellipsometer to perform elliptically polarized light reflection, and measure the phase change Δ and amplitude attenuation under several measurement angles and measurement wavelength ranges.

[0019] S202: Calculate the evaluation function MSE of several measurement angles and measurement wavelength ranges according to the evaluation function MSE formula;

[0020] S203: Obtaining minimum values ​​of the MSEs of the evaluation functions according to the MSEs of the evaluation functions;

[0021] S204: According to the minimum value of the evaluation function MSE, obtain the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE.

[0022] Furthermore, the range of the measurement angle is 0°-90°, and the range of the measurement wavelength is 190nm-1040nm.

[0023] Furthermore, the calculation formula of MSE is:

[0024]

[0025]

[0026] n is the number of measurement wavelengths; m is the number of fitting parameters, E is the data of the measurement point; G is the data corresponding to the fitting point.

[0027] Furthermore, S3 includes the following steps: based on the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected measurement positions, use a spectroscopic ellipsometer to measure the film thickness di of the silicon carbide substrate film layer at the several positions in a single multi-point manner, and at the same time calculate the evaluation function MSEi of the position, and record the film thickness di and the evaluation function MSEi.

[0028] Further, the S4 includes the following steps:

[0029] Based on the evaluation function MSEi of different positions obtained in step S3, the weight coefficient Wi of the film thickness at different positions is determined;

[0030] The formula of the weight coefficient Wi is:

[0031]

[0032] Furthermore, the step S5 includes the following steps: taking the film thickness weight coefficient Wi of several positions obtained in step S4 as a reference, calculating the average film thickness by the formula Extreme film thickness and film thickness uniformity σ.

[0033] Furthermore, the calculation formula of the film thickness mean is:

[0034]

[0035] The calculation formula for the extreme film thickness is:

[0036]

[0037] The calculation formula for the film thickness uniformity is:

[0038]

[0039] The present invention calculates the film thickness mean and film thickness uniformity through an evaluation function and a weight coefficient, and accurately and objectively reflects the film thickness quality on the silicon carbide substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of multi-point single measurement by a spectroscopic ellipsometer according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to better understand the purpose, structure and function of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0042] A method for evaluating film thickness quality of a silicon carbide substrate, comprising:

[0043] S1: selecting a silicon carbide substrate and growing a film layer on the silicon carbide substrate;

[0044] S2: Select several measurement angles and wavelength ranges and use spectroscopic ellipsometer to measure the phase change Δ and amplitude attenuation According to the evaluation function MSE formula, the minimum MSE value is obtained;

[0045] S3: Select several measurement positions, and obtain the film thickness di and evaluation function MSEi at the several positions according to the measurement angle and wavelength range corresponding to the minimum MSE value;

[0046] S4: Based on the evaluation function MSEi, a weight coefficient Wi is obtained;

[0047] S5: Calculate and obtain the film thickness mean and film thickness uniformity according to the formula.

[0048] Specifically, the silicon carbide substrate includes silicon carbide substrates and silicon carbide epitaxial wafers. Substrate sizes include 2-inch, 4-inch, 5-inch, 6-inch, 8-inch, and 10-inch wafers, as well as irregularly sized pieces, that comply with the "GB / T 30866-2014 Test Method for Diameter of Silicon Carbide Single Wafers." In this embodiment, the measurement angle range described in step S102 includes 0°-90°, and the different wavelength ranges include 190nm-1040nm.

[0049] In particular, the film layers grown on the silicon carbide substrate include various film layers grown on the silicon carbide substrate using various physical or chemical processes such as PVD, CVD, and high-temperature oxidation. The grown film layers include single or multilayer films, such as silicon carbide on silicon carbide, silicon oxide on silicon carbide, silicon nitride on silicon carbide, polysilicon on silicon carbide, gallium nitride on silicon carbide, polysilicon on silicon oxide on silicon carbide, silicon nitride on gallium nitride on silicon carbide, silicon oxide on gallium nitride on silicon carbide, and polysilicon on silicon nitride on silicon carbide. In particular, when measuring the film thickness, it must be ensured that the film is transparent or semi-transparent.

[0050] In this embodiment, a 4-inch silicon carbide substrate is taken, and a film layer is grown on the silicon carbide substrate.

[0051] Step S2 includes:

[0052] S201: Selecting several measurement angles and wavelength ranges, performing elliptically polarized light reflection using a single-point single-shot measurement method of a spectroscopic ellipsometer, and measuring phase changes and amplitude attenuation at the several measurement angles and wavelength ranges;

[0053] S202: Calculate the evaluation function MSE of several measurement angles and measurement wavelength ranges according to the evaluation function MSE formula;

[0054] S203: Obtaining minimum values ​​of the MSEs of the evaluation functions according to the MSEs of the evaluation functions;

[0055] S204: According to the minimum value of the evaluation function MSE, obtain the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE.

[0056] In particular, the MSE is calculated as:

[0057]

[0058]

[0059] Where n is the number of measurement wavelengths; m is the number of fitting parameters; E is the data of the measurement point; and G is the data corresponding to the fitting point.

[0060] 3n represents the accumulation of three sets of data from 1 to n, and m is the number of parameters being fitted. The typical repeatability and accuracy of the parameters N, C, and S is 0.001, so the square root needs to be multiplied by 1000.

[0061] In this embodiment, SiO2 of a certain thickness is grown on a silicon carbide substrate using an LPCVD process. In the single-point single-shot measurement mode, the measurement angles are adjusted to 50°, 60°, and 70°, respectively, and the wavelength selection ranges are 190-1040 nm, 320-850 nm, 190-450 nm, and 320-1040 nm, respectively. The minimum value of the evaluation function MSE is 4.3969, corresponding to a measurement angle of 50° and a wavelength range of 190-1040 nm.

[0062]

[0063] Table 1 MSE values ​​at different measurement angles and wavelength ranges

[0064] Step S3 includes: based on the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected measurement positions, using a spectroscopic ellipsometer to measure the film thickness di of the silicon carbide substrate film layer at the several positions in a single multi-point manner, and at the same time calculating the evaluation function MSEi of the position, and recording the film thickness di and the evaluation function MSEi.

[0065] Wherein, i represents the i-th measurement position, di represents the film thickness at the i-th measurement position, and MSEi represents the evaluation function at the i-th measurement position; wherein, i ≥ 2.

[0066] In this embodiment, the fixed measurement angle is 50°, and in the multi-point single measurement mode, 5-point measurement is selected. The specific measurement sequence is as follows: Figure 1 As shown, the directions are from 1 to 5, and the film thickness and MSE data corresponding to the 5 points are shown in Table 2.

[0067] Point Number Film thickness(mm) MSE 1 654.140 7.3309 2 651.021 6.6221 3 651.596 6.7105 4 653.182 7.1722 5 651.153 6.6674

[0068] Table 2 Film thickness and MSE of each point in five-point single measurement: measurement angle is 50°

[0069] The step S4 is to construct a weight coefficient Wi of different positions of the film layer on the silicon carbide substrate for a single multi-point measurement, that is, to determine the weight coefficient Wi of the film thickness at different positions based on the evaluation function MSEi of different positions obtained in step S3; wherein i≥2.

[0070] The specific process of step S4 is to use the minimum value of the evaluation function MSEi of the multi-point single measurement of the silicon carbide upper film layer as MSEmin to construct the weight coefficient Wi, where i represents the i-th measurement position, Wi represents the weight coefficient of the i-th measurement position, and i≥2.

[0071] In particular, the formula of the weight coefficient Wi is:

[0072]

[0073] In this embodiment, the minimum MSE value of 6.6221 obtained in step S3 is taken as MSE min and assigned a weight of 1. The MSEs of other measurement positions are weighted and the weight data of the film thickness at different positions are calculated as shown in Table 3.

[0074] Point Number Film thickness Weight 1 654.140 0.9504 2 651.021 1 3 651.596 0.9995 4 653.182 0.9608 5 651.153 0.9998

[0075] Table 3 Film thickness and weight at each position during single measurement at five points: measuring angle is 50°

[0076] S5: Based on the film thickness weight coefficient Wi of several positions obtained in step S4, the film thickness mean, film thickness extreme value and film thickness uniformity of the film layer on the silicon carbide substrate are calculated by the formula to obtain the film thickness mean Extreme film thickness and film thickness uniformity σ.

[0077] The calculation formula for the mean film thickness is:

[0078]

[0079] The calculation formula for the extreme film thickness is:

[0080]

[0081] The calculation formula for film thickness uniformity is:

[0082]

[0083] In this embodiment, the Wi obtained in step S4 is used as the weight to calculate the average value of the multi-point film thickness, and the obtained values ​​are dmax=651.2702, dmin=621.6946, and the average film thickness is Extreme film thickness The film thickness uniformity σ is 4.6%. From now on, the film thickness quality can be evaluated by the film thickness mean and film thickness uniformity.

[0084] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A method for evaluating film thickness quality of a silicon carbide substrate, characterized in that: The following steps are involved: S1: selecting a silicon carbide substrate and growing a film layer on the silicon carbide substrate; S2: Select several measurement angles and wavelength ranges and use spectroscopic ellipsometer to measure phase changes and amplitude decay , according to the evaluation function MSE formula, the minimum MSE value is obtained; S3: Select several measurement positions, and calculate the film thickness d at several positions according to the measurement angle and wavelength range corresponding to the minimum MSE value. i And the evaluation function MSE i ; S4: Based on the evaluation function MSE i , get the weight coefficient W i ; S5: Calculate and obtain the film thickness mean and film thickness uniformity according to the formula; The evaluation function MSE formula is as follows: The evaluation function MSE formula is as follows: ； in, ; ; ; n is the number of measurement wavelengths; m is the number of fitting parameters; E is the data of the measurement point; G is the data of the corresponding fitting point; is the amplitude attenuation, is the phase change; The weight coefficient W i The formula is as follows: ； in, is the minimum MSE value, is the evaluation function MSE i ; The film thickness uniformity is obtained by the following formula: ； in, is the film thickness uniformity, is the extreme value of film thickness, is the mean film thickness; The film thickness extreme value is obtained by the following formula: ； in, is the maximum value of the product of film thickness and weight coefficient, is the minimum value of the product of film thickness and weight coefficient; The mean film thickness is obtained by the following formula: ； Among them, W i is the weight coefficient, is the film thickness, For the number.

2. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 1, wherein: The silicon carbide substrate includes a silicon carbide substrate sheet and a silicon carbide epitaxial wafer.

3. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 2, wherein: The film layer is at least one layer.

4. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 2, wherein: The step S2 comprises the following steps: S201: Select several measurement angles and wavelength ranges, use the single-point single-shot measurement method of the spectroscopic ellipsometer to perform elliptically polarized light reflection, and measure the phase changes under several measurement angles and measurement wavelength ranges. and amplitude decay ; S202: Calculate the evaluation function MSE of several measurement angles and measurement wavelength ranges according to the evaluation function MSE formula; S203: Obtaining minimum values ​​of the MSEs of the evaluation functions according to the MSEs of the evaluation functions; S204: According to the minimum value of the evaluation function MSE, obtain the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE.

5. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 4, wherein: The measurement angle ranges from 0° to 90°, and the wavelength ranges from 190 nm to 1040 nm.

6. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 4, wherein: The step S3 comprises the following steps: based on the measurement angle and wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected measurement positions, using a spectroscopic ellipsometer to measure the film thickness d of the silicon carbide substrate film layer at the selected positions in a single multi-point manner; i , and calculate the evaluation function MSE of the position at the same time i , record the film thickness d i And the evaluation function MSE i .

7. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 6, wherein: The step S4 comprises the following steps: The different position evaluation function MSE obtained in step S3 is used i As a benchmark, determine the weight coefficient W of the film thickness at different positions i .

8. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 7, wherein: The step S5 includes the following steps: using the film thickness weight coefficient W of the plurality of positions obtained in step S4 i As a benchmark, the average film thickness is calculated by the formula , film thickness extreme value and film thickness uniformity .

Images