Etching selectivity measurement method for silicon carbide dielectric layer

Abstract

A method for measuring the etching selectivity of a silicon carbide dielectric layer belongs to the field of semiconductor technology and includes the following steps: measuring the dielectric film thickness H1 of the dielectric layer on the silicon carbide using a spectroscopic ellipsometer and calculating an evaluation function MSE1 of the dielectric film thickness using a formula; fabricating a mask layer and measuring the mask layer thickness Ht using a step profiler; based on the mask layer thickness Ht measured in step S2, measuring the mask layer thickness Hy using a spectroscopic ellipsometer and calculating an evaluation function MSEy of the mask layer thickness using a formula; etching the silicon carbide dielectric layer containing the mask, measuring the step depth Het after etching using a step profiler and the mask layer thickness Hey after etching using an ellipsometer; and calculating the etching selectivity according to a formula. This method makes the thickness measurement of the silicon carbide mask layer more accurate during the etching process, thereby making the etching process debugging results of the dielectric layer on the silicon carbide with respect to the mask layer more reliable.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for measuring the etching selectivity of a silicon carbide dielectric layer. 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] The dry etching process mainly refers to the use of ions or free radicals in the plasma generated by low-voltage discharge to chemically react with the material or achieve the purpose of etching through physical effects such as bombardment. Its basic goal is to accurately replicate the mask pattern on the coated substrate or dielectric layer. The main parameters of concern in dry etching are etching selectivity and etching morphology. During the debugging of the selective etching process of the silicon carbide dielectric layer, considering the cost of silicon carbide wafers and the time and labor-intensive SEM cross-sectional slice observation, a step meter and ellipsometer are often used in combination to measure and calculate the etching selectivity. However, the existing ellipsometer has a weak ability to measure multilayer films. As the dielectric layer on the silicon carbide substrate is etched, the thickness of the mask layer continues to change. Measuring the mask layer thickness only with an ellipsometer will cause the measurement result to deviate significantly from the actual value. This method uses the mask layer measured by the step meter as the initial parameter and the thickness of the dielectric layer on the silicon carbide as the intermediate variable. The dielectric layer thickness during the ellipsometer measurement process is adjusted so that the pre-etching mask layer thickness measured by the ellipsometer is equal to the pre-etching step thickness measured by the step meter. Based on the determined thickness of the dielectric layer on the silicon carbide, the thickness of the mask layer on the dielectric layer on the silicon carbide after etching is measured.

[0004] In the calculation process of mathematical statistics correction sample variance, , where n represents the number of samples of the fitted mean and 1 represents the sample mean of the fitted parameter. This formula can evaluate the degree of data variation. The smaller the MSE value, the better the accuracy of the prediction model in describing the experimental data. Summary of the Invention

[0005] The present invention aims to provide a method for measuring the etching selectivity of a silicon carbide dielectric layer, so as to solve the problem of accurately measuring the etching selectivity of a dielectric layer on silicon carbide relative to a mask layer.

[0006] A method for measuring the etching selectivity of a silicon carbide dielectric layer includes the following steps:

[0007] Step S1: using a spectroscopic ellipsometer to measure the dielectric film thickness H1 of the dielectric layer on the silicon carbide, and calculating the evaluation function MSE1 of the dielectric film thickness by a formula;

[0008] Step S2: fabricating a mask layer and measuring the thickness Ht of the mask layer using a step profiler;

[0009] Step S3: Based on the mask layer thickness Ht measured in step S2, the mask layer thickness Hy is measured using a spectroscopic ellipsometer, and an evaluation function MSEy of the mask layer thickness is calculated using a formula;

[0010] Step S4: etching the silicon carbide upper dielectric layer containing the mask, measuring the step depth Het after etching using a step profiler, measuring the thickness Hey of the mask layer after etching using an ellipsometer, and calculating an evaluation function MSEey of the thickness of the mask layer after etching according to the formula;

[0011] Step S5: Calculate the etching selectivity according to the formula.

[0012] Furthermore, the step S1 includes the following steps:

[0013] S101: selecting a silicon carbide substrate, and growing a dielectric layer on the silicon carbide substrate;

[0014] S102: Using a spectroscopic ellipsometer to measure the dielectric film thickness H1 of the dielectric layer, and obtain the amplitude attenuation φ and the phase change Δ;

[0015] S103: According to the obtained amplitude attenuation φ and phase change Δ, an evaluation function MSE1 of the dielectric film thickness is calculated by a formula.

[0016] Furthermore, the evaluation function MSE formula is:

[0017] ;

[0018] N = cos(2φ);

[0019] C = cos (2φ) cos (Δ);

[0020] S = sin(2φ)sin(Δ);

[0021] Where 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; Δ and φ are the data detected by the spectroscopic ellipsometer, Δ is the phase change and φ is the amplitude attenuation.

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

[0023] Furthermore, the value of the evaluation function MSE1 of the dielectric film thickness H1 in step S1 is less than 20.

[0024] Furthermore, the measuring length of the step profiler includes 0 μm~20000 μm, the probe pressure is 0 mg~15 mg, and the measuring time is 0 s~60 s.

[0025] Furthermore, in step S3 , the mask layer thickness Hy measured by the spectroscopic ellipsometer and the mask thickness Ht measured by the step profiler satisfy the formula |Ht-Hy| / Ht≤2%, and the value of the evaluation function MSEy of the mask layer thickness Hy is less than 20.

[0026] Furthermore, the position measured by the step profiler in step S4 is the same as the position measured by the step profiler in step S3, and the measurement length, probe pressure and measurement time used by the step profiler in step S4 are also the same as the measurement length, probe pressure and measurement time used in step S3.

[0027] Furthermore, the value of the evaluation function MSEey of the thickness Hey of the mask layer after etching measured in step S4 is less than 20.

[0028] Furthermore, the etching selectivity ratio formula is: (Het-Hey) / (Hy-Hey).

[0029] The method makes the thickness measurement of the mask layer on the silicon carbide more accurate during the etching process, thereby making the selection of the dielectric layer on the silicon carbide relative to the mask layer and the etching process debugging result more reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the mask layer structure on the dielectric layer on the silicon carbide substrate;

[0031] Figure 2 Schematic diagram of step measurement using a step gauge. DETAILED DESCRIPTION

[0032] 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.

[0033] A method for measuring the etching selectivity of a silicon carbide dielectric layer comprises the following steps:

[0034] Step S1: selecting a silicon carbide substrate, growing a dielectric layer on the silicon carbide substrate, using a spectroscopic ellipsometer to measure the dielectric film thickness H1 of the dielectric layer at a single point and once, and calculating an evaluation function MSE1 of the dielectric film thickness using a formula;

[0035] Preferably, the silicon carbide substrate described in step S1 includes a silicon carbide substrate and a silicon carbide epitaxial wafer, and the silicon carbide substrate is a regular 2-inch, 4-inch, 5-inch, 6-inch, 8-inch, or 10-inch wafer with a size that complies with "GB / T 30866-2014 Test Method for Diameter of Silicon Carbide Single Wafers", or an irregular fragment;

[0036] Preferably, the dielectric layer on the silicon carbide substrate described in step S1 is a different film layer grown on the silicon carbide substrate using various physical or chemical processes such as PVD, CVD, and high-temperature oxidation. The grown film layer includes a single film or a multilayer film on the silicon carbide substrate, such as silicon carbide on silicon carbide, silicon oxide on silicon carbide, silicon nitride on silicon carbide, polycrystalline silicon on silicon carbide, gallium nitride on silicon carbide, polycrystalline silicon on silicon oxide on silicon carbide, silicon nitride on gallium nitride on silicon carbide, silicon oxide on gallium nitride on silicon carbide, and polycrystalline silicon on silicon nitride on silicon carbide. The film thickness must ensure light transmission or semi-transparency.

[0037] The measurement angle range of the spectroscopic ellipsometer is 0°~90°, and the wavelength range is 190nm~1040nm.

[0038] The evaluation function MSE formula is:

[0039]

[0040] N=cos(2φ)

[0041] C = cos (2φ) cos (Δ)

[0042] S=sin(2φ)sin(Δ)

[0043] Where 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; Δ and φ are the data detected by the spectroscopic ellipsometer, Δ is the phase change and φ is the amplitude attenuation.

[0044] 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.

[0045] In particular, the value of the evaluation function MSE1 for the dielectric film thickness H1 must be less than 20.

[0046] Step S2: fabricating a mask layer and measuring the thickness Ht of the mask layer using a step profiler.

[0047] The mask layer described in step S2 is a mask layer prepared on the dielectric layer on the silicon carbide substrate using various physical or chemical processes such as photolithography, PVD, CVD, and high-temperature oxidation. The prepared mask layer includes a silicon oxide layer, a nitride layer, a photoresist layer, and a metal layer, and the mask layer must ensure light transmission or semi-transmission;

[0048] The mask layer on the dielectric layer on the silicon carbide substrate described in step S2 refers to the presence of steps that can be measured by a step meter probe. The steps include pits or protrusions. The radius of the step meter probe varies from 0.2μm, 0.7μm, 2μm to 5μm. The width of the pits or protrusions in the mask layer must be greater than the probe diameter.

[0049] Preferably, the measuring length of the step profiler is 0 μm to 20,000 μm, the probe pressure is 0 mg to 15 mg, and the measuring time is 0 s to 60 s.

[0050] The specific process of step profiler measurement in step S2 is to select different measurement lengths, probe pressures and measurement times, insert the probe where there are steps in the mask layer, and obtain the step depth Ht, which is the thickness of the mask layer measured by the step profiler.

[0051] Step S3: Based on the mask layer thickness Ht measured by the step analyzer in step S2, the mask layer thickness Hy is measured by a spectroscopic ellipsometer at a single point and once, and an evaluation function MSEy of the mask layer thickness is obtained.

[0052] In particular, the mask layer thickness Hy measured by the spectroscopic ellipsometer and the mask thickness Ht measured by the step profiler must satisfy the formula |Ht-Hy| / Ht≤2%; and the value of the evaluation function MSEy of the mask layer thickness H ellipsometric must be less than 20.

[0053] Step S4: Etch the silicon carbide upper dielectric layer containing the mask, use a step meter to measure the step depth Het after etching, use an ellipsometer to measure the thickness Hey of the mask layer after etching at a single point and single time, and at the same time calculate the evaluation function MSEey of the mask layer thickness after etching according to the evaluation function MSE formula.

[0054] In particular, the value of the evaluation function MSEey of the mask layer thickness Hey after etching must be less than 20; the measurement position is the same mask step measurement position in step S3, and the measurement length, probe pressure and measurement time used are also the same as the measurement length, probe pressure and measurement time in step S3.

[0055] Step S5: Calculate the etching selectivity according to the formula.

[0056] The etching selectivity ratio formula is: (Het-Hey) / (Hy-Hey).

[0057] Specifically, step S1 is: select a 4-inch silicon carbide substrate, use the LPCVD process to grow a dielectric layer SiO2 of a certain thickness on the substrate, and use an ellipsometer to measure the film thickness of SiO2 on the silicon carbide to be 2880nm when the measurement angle is 70° and the wavelength range is 190~1040nm. According to the formula, the evaluation function MSE1 of the dielectric film thickness is calculated to be 7.8. The value of the evaluation function MSE1 is less than 20, and the next step is performed.

[0058] Step S2 is: using a photolithography process to make a mask layer and a photolithography pattern on the silicon oxide dielectric layer on the silicon carbide, using a step meter to measure the thickness of the mask layer, that is, measuring the step depth where there is no photoresist blocking it. The measurement length is selected as 400μm, the probe pressure is selected as 3mg, and the measurement time is selected as 6s. The thickness Ht of the photoresist mask layer is measured to be 1178nm.

[0059] The step S3 comprises: based on the thickness Ht of the photoresist mask measured by the step profiler in step S2, the thickness of the photoresist mask is measured by an ellipsometer to be 1166 nm; then, based on the data measured by the ellipsometer, an evaluation function of 4.5 is obtained by a calculation formula, and the evaluation function 4.5≤20; finally, according to the formula |Ht-Hy| / Ht=1.0%≤2%, the requirement is met;

[0060] Step S4 is: etching SiO2 using an etching process. After etching is completed, a step profiler is used to measure the step depth without the photoresist mask layer blocking it. The measurement length is selected as 400 μm, the probe pressure is selected as 3 mg, and the measurement time is selected as 6 s. The step depth is measured to be 2806 nm. The thickness of the photoresist mask after etching is measured using an ellipsometer and is 186 nm. The evaluation function is 6.8≤20.

[0061] Step S5 is: based on the photoresist thickness before etching measured by the ellipsometer in step S3 of 1166nm, the photoresist thickness after etching measured by the ellipsometer in step S4 of 186nm, and the step depth without photoresist mask after etching measured by the step profiler of 2806nm, the etching selectivity ratio of silicon oxide to photoresist is calculated to be 2.67.

[0062] 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 measuring the etching selectivity of a silicon carbide dielectric layer, characterized in that: The following steps are involved: Step S1: using a spectroscopic ellipsometer to measure the dielectric film thickness H1 of the dielectric layer on the silicon carbide, and calculating the evaluation function MSE1 of the dielectric film thickness by a formula; Step S2: fabricating a mask layer and measuring the thickness Ht of the mask layer using a step profiler; Step S3: Based on the mask layer thickness Ht measured in step S2, the mask layer thickness Hy is measured using a spectroscopic ellipsometer, and an evaluation function MSEy of the mask layer thickness is calculated using a formula; Step S4: etching the silicon carbide upper dielectric layer containing the mask, measuring the step depth Het after etching using a step profiler, measuring the thickness Hey of the mask layer after etching using an ellipsometer, and calculating an evaluation function MSEey of the thickness of the mask layer after etching according to the formula; Step S5: Calculate the etching selectivity according to the formula; The calculation formula of the evaluation function MSE is: ； N = cos(2φ); C = cos (2φ) cos (Δ); S = sin(2φ)sin(Δ); Where 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; Δ and φ are the data detected by spectroscopic ellipsometer, Δ is the phase change, and φ is the amplitude attenuation; The value of the evaluation function MSE1 of the dielectric film thickness H1 in step S1 must be less than 20; The mask layer thickness Hy measured by the spectroscopic ellipsometer in step S3 and the mask layer thickness Ht measured by the step profiler satisfy the formula: |Ht-Hy| / Ht≤2%, And the value of the evaluation function of the mask layer thickness Hy must be less than 20; The value of the evaluation function MSEey of the thickness Hey of the mask layer after etching measured in step S4 must be less than 20; The etching selectivity ratio is calculated as follows: (Het-Hey) / (Hy-Hey).

2. The method for measuring the etching selectivity of a silicon carbide dielectric layer according to claim 1, wherein: The step S1 comprises the following steps: S101: selecting a silicon carbide substrate, and growing a dielectric layer on the silicon carbide substrate; S102: Using a spectroscopic ellipsometer to measure the dielectric film thickness H1 of the dielectric layer, and obtain the amplitude attenuation φ and the phase change Δ; S103: According to the obtained amplitude attenuation φ and phase change Δ, an evaluation function MSE1 of the dielectric film thickness is calculated by a formula.

3. The method for measuring etching selectivity of a silicon carbide dielectric layer according to claim 1, wherein: The measurement angle range of the spectroscopic ellipsometer is 0°~90°, and the wavelength range is 190nm~1040nm.

4. The method for measuring etching selectivity of a silicon carbide dielectric layer according to claim 1, wherein: The measuring length of the step profiler ranges from 0 μm to 20,000 μm, the probe pressure ranges from 0 mg to 15 mg, and the measuring time ranges from 0 s to 60 s.

5. The method for measuring etching selectivity of a silicon carbide dielectric layer according to claim 4, wherein: The position measured by the step profiler in step S4 is the same as that measured by the step profiler in step S3, and the measurement length, probe pressure, and measurement time used by the step profiler in step S4 are also the same as those in step S3.

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