CN114493139A - Method for evaluating film thickness quality of silicon carbide substrate - Google Patents
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- 239000000758 substrate Substances 0.000 title claims abstract description 53
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- 238000011156 evaluation Methods 0.000 claims abstract description 47
- 238000001228 spectrum Methods 0.000 claims abstract description 11
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- 238000000572 ellipsometry Methods 0.000 claims description 3
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- 238000013441 quality evaluation Methods 0.000 abstract description 5
- 239000004065 semiconductor Substances 0.000 abstract description 5
- 239000010408 film Substances 0.000 description 88
- 239000010410 layer Substances 0.000 description 13
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 8
- 238000005516 engineering process Methods 0.000 description 6
- 229910052814 silicon oxide Inorganic materials 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 4
- 229920005591 polysilicon Polymers 0.000 description 4
- 229910002601 GaN Inorganic materials 0.000 description 3
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 3
- 229910052581 Si3N4 Inorganic materials 0.000 description 3
- 238000005229 chemical vapour deposition Methods 0.000 description 3
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
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- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
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- 238000004518 low pressure chemical vapour deposition Methods 0.000 description 2
- 229910052682 stishovite Inorganic materials 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 235000012431 wafers Nutrition 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 244000000626 Daucus carota Species 0.000 description 1
- 235000002767 Daucus carota Nutrition 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
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- 238000000407 epitaxy Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000007888 film coating Substances 0.000 description 1
- 238000009501 film coating Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
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- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 239000005543 nano-size silicon particle Substances 0.000 description 1
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- 229920006395 saturated elastomer Polymers 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000002210 silicon-based material Substances 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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Abstract
A film thickness quality evaluation method of a silicon carbide substrate belongs to the technical field of semiconductors and comprises the following steps: s1, selecting a silicon carbide substrate, and performing film growth on the silicon carbide substrate; s2, selecting a plurality of measuring angles and wavelength ranges, measuring phase change and amplitude attenuation by using a spectrum ellipsometer, and obtaining an MSE minimum value according to an evaluation function MSE formula; s3, selecting a plurality of measured positions, and obtaining film thickness di and an evaluation function MSEi of the positions according to the measurement angle and the wavelength range corresponding to the MSE minimum value; s4, obtaining a weight coefficient Wi based on the evaluation function MSEi; and S5, calculating according to the formula to obtain the film thickness average value and the film thickness uniformity. According to the invention, the film thickness mean value and the film thickness uniformity are calculated through the evaluation function and the weight coefficient, and the film thickness quality on the silicon carbide substrate is accurately and objectively reflected.
Description
Technical Field
The invention belongs to the field of semiconductors, and particularly relates to a film thickness quality evaluation method for a silicon carbide substrate.
Background
The third-generation semiconductor material silicon carbide has the characteristics of high critical breakdown electric field, high thermal conductivity, high saturated electron drift velocity and the like, so that the third-generation semiconductor material silicon carbide can play a more excellent role than a silicon material in the fields of high temperature, high pressure and high frequency. In the fields of power electronics, radio frequency devices and photoelectric devices, MOSFETs, HEMTs and the like using silicon carbide as a substrate are being increasingly studied.
The semiconductor processing technology mainly forms pattern stacks of different layers on an epitaxial wafer through technologies such as photoetching, etching, thin film, interface oxidation and the like, and finally generates a finally usable chip through scribing, chip testing and packaging. In the thin film and interface oxidation process, different processing techniques can obtain different coating films, such as sputtering carbon films and metal films by using a PVD (physical vapor deposition) technology, growing silicon oxide and polysilicon films by using a CVD (chemical vapor deposition) technology and oxidizing by using a high-temperature oxidation technology to generate nano silicon oxide and silicon oxide films. For the measurement of different films generated, the measurement tools commonly used at present are a film thickness meter and an ellipsometer. The film thickness meter is mainly used for measuring semitransparent and opaque films, and for the transparent and semitransparent films with thinner thickness, an ellipsometer is mainly used for measuring.
The ellipsometer is classified into a laser ellipsometer and a spectroscopic ellipsometer according to the form of light generated by a light source thereof, and the laser ellipsometer is only suitable for measuring a fixed film layer in industrial mass production due to a single measurement light source and has low measurement accuracy. The spectrum ellipsometer covers the long-wave band light source from ultraviolet light, visible light to infrared light, so that the spectrum ellipsometer ensures complete types and high precision of the measured film spectrum, and is very suitable for the technical research and development process.
Ellipsometer film thickness measurement on silicon substrates has been effectively verified, and research on ellipsometer film thickness measurement on silicon carbide substrates and epitaxy is still deepening due to anisotropy of silicon carbide materials and coating defects of different processing technologies. In the measurement process of the traditional spectrum ellipsometer, the film thickness attribute cannot be comprehensively and objectively reflected only by data obtained by unit measurement, different positions need to be manually selected and recalibrated each time during multiple measurements, and the time cost is high. The method combines a single-point single measurement mode and a multi-point single measurement mode of the ellipsometer, takes the film thickness mean value and the uniformity as optimization indexes, and expresses the film coating quality on the silicon carbide substrate by the optimized film thickness mean value and the optimized uniformity, thereby more accurately and objectively reflecting the film thickness property on the silicon carbide substrate.
Due to the anisotropic effect of silicon carbide, the thickness measurement data of the silicon carbide substrate can be greatly deviated due to the differences of the thickness and crystal plane orientation of silicon carbide substrate sheets or epitaxial wafers provided by different manufacturers and the uncertainty of self defects such as micropipes and carrot bodies. In addition, the measurement of the film thickness in this method is performed only by a single-point multiple measurement, and the uniformity of the film thickness on the silicon carbide substrate cannot be reflected.
Disclosure of Invention
The invention aims to provide a film thickness quality evaluation method of a silicon carbide substrate, which aims to solve the technical problem of film thickness quality evaluation of the silicon carbide substrate.
In order to solve the technical problems, the specific technical scheme of the invention is as follows:
the film thickness quality evaluation method of the silicon carbide substrate comprises the following steps:
s1, selecting a silicon carbide substrate, and performing film growth on the silicon carbide substrate;
s2 selecting several measuring angles and wavelength ranges, and measuring phase change delta and amplitude attenuation by using spectroscopic ellipsometer
Obtaining an MSE minimum value according to an evaluation function MSE formula;
s3, selecting a plurality of positions to be measured, and obtaining film thickness di and an evaluation function MSEi of the positions according to a measurement angle and a wavelength range corresponding to the MSE minimum value;
s4, obtaining a weight coefficient Wi based on the evaluation function MSEi;
and S5, calculating according to the formula to obtain the film thickness average value and the film thickness uniformity.
Further, the silicon carbide substrate comprises a silicon carbide substrate sheet and a silicon carbide epitaxial sheet.
Further, the film layer is at least one layer.
Further, the S2 includes the following steps:
s201: selecting a plurality of measurement angles and wavelength ranges, performing ellipsometry reflection by using a single-point single-measurement method of a spectrum ellipsometer, and measuring to obtain phase change delta and amplitude attenuation under the measurement angles and the measurement wavelength ranges
S202, calculating to obtain evaluation functions MSE of a plurality of measurement angles and measurement wavelength ranges according to an evaluation function MSE formula;
s203: obtaining the minimum value of the evaluation functions MSE according to the evaluation functions MSE;
s204: and obtaining a measurement angle and a wavelength range corresponding to the minimum value of the evaluation function MSE according to the minimum value of the evaluation function MSE.
Further, the measuring angle ranges from 0 to 90 degrees, and the measuring wavelength ranges from 190nm to 1040 nm.
Further, the calculation formula of MSE is:
n is the number of measurement wavelengths; m is the number of fitting parameters, and E is the data of the measuring points; g is the data corresponding to the fitting point.
Further, the S3 includes the following steps: based on the measurement angle and the wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected and measured positions, using a spectrum ellipsometer to measure the film thickness di of the silicon carbide substrate film layer at the positions in a multi-point single time, meanwhile, calculating the evaluation function MSEi at the position, and recording the film thickness di and the evaluation function MSEi.
Further, the S4 includes the following steps:
determining the weight coefficients Wi of the film thicknesses at different positions by taking the evaluation functions MSEi at different positions obtained in the step S3 as the reference;
the formula of the weight coefficient Wi is:
further, the S5 includes the following steps: using the film thickness weight coefficients Wi of the plurality of positions obtained in the step S4 as a reference, and calculating by a formula to obtain a film thickness average value
Extreme value of film thickness
And film thickness uniformity σ.
Further, the calculation formula of the film thickness mean value is as follows:
the calculation formula of the film thickness extreme value is as follows:
the calculation formula of the film thickness uniformity is as follows:
according to the invention, the film thickness mean value and the film thickness uniformity are calculated through the evaluation function and the weight coefficient, and the film thickness quality on the silicon carbide substrate is accurately and objectively reflected.
Drawings
FIG. 1 is a schematic diagram of a spectroscopic ellipsometer for a single measurement at multiple points in accordance with an embodiment of the present invention.
Detailed Description
For a better understanding of the objects, structure and function of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
A method for evaluating the film thickness quality of a silicon carbide substrate comprises the following steps:
s1, selecting a silicon carbide substrate, and performing film growth on the silicon carbide substrate;
s2 selecting several measuring angles and wavelength ranges, and measuring phase change delta and amplitude attenuation by using spectroscopic ellipsometer
Obtaining an MSE minimum value according to an evaluation function MSE formula;
s3, selecting a plurality of positions to be measured, and obtaining film thickness di and an evaluation function MSEi of the positions according to a measurement angle and a wavelength range corresponding to the MSE minimum value;
s4, obtaining a weight coefficient Wi based on the evaluation function MSEi;
and S5, calculating according to the formula to obtain the film thickness average value and the film thickness uniformity.
Specifically, the silicon carbide substrate comprises a silicon carbide substrate sheet and a silicon carbide epitaxial sheet, and the substrate size comprises 2 inches, 4 inches, 5 inches, 6 inches, 8 inches, 10 inches and irregular fragments which meet the rule of GB/T30866-2014 diameter test method for silicon carbide single crystal sheets. In this embodiment, the measurement angle range described in step S102 includes 0 ° to 90 °, and the different wavelength ranges include 190nm to 1040 nm.
In particular, the film layer grown on the silicon carbide substrate includes different film layers grown on a silicon carbide substrate by various physical or chemical processes such as PVD, CVD, high temperature oxidation, etc., wherein the film layer grown includes a single layer film or a plurality of layers of 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 carbide, silicon nitride on gallium nitride on silicon carbide, silicon oxide on gallium nitride on silicon carbide, polysilicon on silicon nitride on silicon carbide. In particular, the thickness of the film is measured to ensure that the film is transparent or semi-transparent.
In this example, a 4-inch silicon carbide substrate piece was taken, and film growth was performed on the silicon carbide substrate.
Step S2 includes:
s201: selecting a plurality of measurement angles and wavelength ranges, performing ellipsometry reflection by using a single-point single-measurement method of a spectrum ellipsometer, and measuring to obtain phase change and amplitude attenuation under the measurement angles and the measurement wavelength ranges;
s202, calculating to obtain evaluation functions MSE of a plurality of measurement angles and measurement wavelength ranges according to an evaluation function MSE formula;
s203: obtaining the minimum value of the evaluation functions MSE according to the evaluation functions MSE;
s204: and obtaining a measurement angle and a wavelength range corresponding to the minimum value of the evaluation function MSE according to the minimum value of the evaluation function MSE.
In particular, the formula for computing MSE is:
wherein n is the number of measurement wavelengths; m is the number of fitting parameters, and E is the data of the measuring points; g is the data corresponding to the fitting point.
3n represents the data accumulation, here 3 sets 1 to n, and m is the number of parameters fitted. N, C, S is typically 0.001 in repeatability and accuracy, so the root is started and multiplied by 1000.
In the embodiment, SiO2 with a certain thickness is grown on a silicon carbide substrate by adopting an LPCVD (low pressure chemical vapor deposition) process, under a single-point single-time measurement mode, the measurement angles are respectively adjusted to be 50 degrees, 60 degrees and 70 degrees, the wavelength selection ranges are respectively 190-1040 nm, 320-850 nm, 190-450 nm and 320-1040 nm, the minimum value of an evaluation function MSE is 4.3969, the corresponding measurement angle is 50 degrees, and the wavelength range is 190-1040 nm;
TABLE 1 MSE values at different measurement angles and wavelength ranges
Step S3 includes: based on the measurement angle and the wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected and measured positions, using a spectrum ellipsometer to measure the film thickness di of the silicon carbide substrate film layer at the positions in a multi-point single time, meanwhile, calculating the evaluation function MSEi at the position, and recording the film thickness di and the evaluation function MSEi.
Wherein i represents the ith measurement position, di represents the film thickness of the ith measurement position, and MSEi represents the evaluation function of the ith measurement position; wherein i is more than or equal to 2.
In this embodiment, the fixed measurement angle is 50 °, 5-point measurement is selected in a multi-point single measurement mode, the specific measurement sequence process is shown in fig. 1, the directions are sequentially from 1 to 5, and the film thickness and MSE data corresponding to the 5 points are shown in table 2.
| Point numbering | Film thickness (mm) | |
| 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 |
Table 2 five-point single measurement of film thickness and MSE at each point: the measured angle is 50 °
S4 is to construct weight coefficients Wi of different positions of a film layer on a silicon carbide substrate for multipoint single measurement, namely the weight coefficients Wi of film thicknesses of different positions are determined by taking evaluation functions MSEi of different positions obtained in the step S3 as a reference; wherein i is more than or equal to 2.
The specific process of step S4 is to construct the weight coefficient Wi with the minimum value of the evaluation function MSEi of the multipoint single measurement silicon carbide film layer as msemin. Wherein i represents the ith measurement position, Wi represents the weighting coefficient of the ith measurement position, and i is more than or equal to 2.
In particular, the formula of the weight coefficient Wi is:
in this embodiment, the minimum MSE value 6.6221 obtained in step S3 is referred to as MSE min, a weight 1 is given, MSEs at other measurement positions are subjected to weight matching, and weight data at different positions under different film thicknesses are calculated and obtained as shown in table 3.
| Point numbering | Film thickness | Weight of |
| 1 | 654.140 | 0.9504 |
| 2 | 651.021 | 1 |
| 3 | 651.596 | 0.9995 |
| 4 | 653.182 | 0.9608 |
| 5 | 651.153 | 0.9998 |
Table 3 film thickness and weight at each position for five single measurements: the measured angle is 50 °
S5: calculating the film thickness mean value, the film thickness extreme value and the film thickness uniformity of the film layer on the silicon carbide substrate by using the film thickness weight coefficients Wi of the positions obtained in the step S4 as the reference through a formula to obtain the film thickness mean value
Extreme value of film thickness
And film thickness uniformity σ.
Wherein, the calculation formula of the film thickness mean value is as follows:
the calculation formula of the film thickness extreme value is as follows:
the calculation formula of the film thickness uniformity is as follows:
in this embodiment, Wi obtained in step S4 is used as a weight to calculate a multipoint film thickness average value, dmax is 651.2702, dmin is 621.6946, and the film thickness average value is obtained
Extreme value of film thickness
The film thickness uniformity σ was 4.6%. From this point on, the film thickness quality can be evaluated by the film thickness average and film thickness uniformity.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (10)
1. The method for evaluating the film thickness quality of the silicon carbide substrate is characterized by comprising the following steps of:
s1, selecting a silicon carbide substrate, and performing film growth on the silicon carbide substrate;
s2 selecting several measuring angles and wavelength ranges, and measuring phase change delta and amplitude attenuation by using spectroscopic ellipsometer
Obtaining an MSE minimum value according to an evaluation function MSE formula;
s3, selecting a plurality of positions to be measured, and obtaining film thickness di and an evaluation function MSEi of the positions according to a measurement angle and a wavelength range corresponding to the MSE minimum value;
s4, obtaining a weight coefficient Wi based on the evaluation function MSEi;
and S5, calculating according to the formula to obtain the film thickness average value and the film thickness uniformity.
2. The method of 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 sheet.
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 includes the steps of:
s201: selecting a plurality of measurement angles and wavelength ranges, performing ellipsometry reflection by using a single-point single-measurement method of a spectrum ellipsometer, and measuring to obtain phase change delta and amplitude attenuation under the measurement angles and the measurement wavelength ranges
S202, calculating to obtain evaluation functions MSE of a plurality of measurement angles and measurement wavelength ranges according to an evaluation function MSE formula;
s203: obtaining the minimum value of the evaluation functions MSE according to the evaluation functions MSE;
s204: and obtaining a measurement angle and a wavelength range corresponding to the minimum value of the evaluation function MSE according 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 is in a range of 0 ° to 90 °, and the wavelength is in a range of 190nm to 1040 nm.
6. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 4, wherein the calculation formula of MSE is:
n is the number of measurement wavelengths; m is the number of fitting parameters, and E is the data of the measuring points; g is the data corresponding to the fitting point.
7. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 4, wherein the step S3 includes the steps of: based on the measurement angle and the wavelength range corresponding to the minimum value of the evaluation function MSE, according to the selected and measured positions, using a spectrum ellipsometer to measure the film thickness di of the silicon carbide substrate film layer at the positions in a multi-point single time, meanwhile, calculating the evaluation function MSEi at the position, and recording the film thickness di and the evaluation function MSEi.
8. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 7, wherein the step S4 includes the steps of:
determining the weight coefficients Wi of the film thicknesses at different positions by taking the evaluation functions MSEi at different positions obtained in the step S3 as the reference;
the formula of the weight coefficient Wi is:
9. the method for evaluating film thickness quality of a silicon carbide substrate according to claim 8, wherein the step S5 includes the steps of: using the film thickness weight coefficients Wi of the plurality of positions obtained in the step S4 as a reference, and calculating by a formula to obtain a film thickness average value
Extreme value of film thickness
And film thickness uniformity σ.
10. The method for evaluating film thickness quality of a silicon carbide substrate according to claim 9, wherein the calculation formula of the film thickness mean value is:
the calculation formula of the film thickness extreme value is as follows:
the calculation formula of the film thickness uniformity is as follows:
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