CN108180879A - The valued methods and preparation method of ultra-thin silica membrane print - Google Patents
The valued methods and preparation method of ultra-thin silica membrane print Download PDFInfo
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- CN108180879A CN108180879A CN201711243418.5A CN201711243418A CN108180879A CN 108180879 A CN108180879 A CN 108180879A CN 201711243418 A CN201711243418 A CN 201711243418A CN 108180879 A CN108180879 A CN 108180879A
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 243
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 121
- 238000000034 method Methods 0.000 title claims abstract description 39
- 238000002360 preparation method Methods 0.000 title claims abstract description 7
- 239000012528 membrane Substances 0.000 title abstract 3
- 239000000758 substrate Substances 0.000 claims abstract description 72
- 238000004140 cleaning Methods 0.000 claims abstract description 46
- 238000005259 measurement Methods 0.000 claims abstract description 34
- 230000010287 polarization Effects 0.000 claims description 97
- 235000012239 silicon dioxide Nutrition 0.000 claims description 87
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 32
- 239000000243 solution Substances 0.000 claims description 31
- 239000012153 distilled water Substances 0.000 claims description 28
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 28
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 16
- 239000006185 dispersion Substances 0.000 claims description 16
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 15
- 230000003647 oxidation Effects 0.000 claims description 15
- 238000007254 oxidation reaction Methods 0.000 claims description 15
- 239000010703 silicon Substances 0.000 claims description 15
- 229910052710 silicon Inorganic materials 0.000 claims description 14
- 238000005406 washing Methods 0.000 claims description 12
- 238000011156 evaluation Methods 0.000 claims description 10
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 8
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 8
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 8
- 238000004364 calculation method Methods 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 8
- 239000011259 mixed solution Substances 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 239000004065 semiconductor Substances 0.000 abstract description 3
- 239000002131 composite material Substances 0.000 abstract 1
- 239000010408 film Substances 0.000 description 81
- 239000010409 thin film Substances 0.000 description 10
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 229910052786 argon Inorganic materials 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 2
- 230000036962 time dependent Effects 0.000 description 2
- 238000000342 Monte Carlo simulation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B21/00—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant
- G01B21/02—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness
- G01B21/08—Measuring arrangements or details thereof, where the measuring technique is not covered by the other groups of this subclass, unspecified or not relevant for measuring length, width, or thickness for measuring thickness
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Testing Or Measuring Of Semiconductors Or The Like (AREA)
Abstract
The present invention is suitable for technical field of semiconductors, provides a kind of valued methods and preparation method of ultra-thin silica membrane print.The valued methods include：Substrate is cleaned in cleaning solution；The upper surface growth thickness of the substrate after cleaning is less than 10 nanometers of silica membrane；Definite value region is chosen, n measurement point is chosen in the definite value region；Determine the thickness evenness of the print；Determine the thickness stability of the print；Determine the partial uncertainty that measurer for thickness introduces；The Composite Seismogram and expanded uncertainty of the print are determined according to the partial uncertainty, the thickness evenness and the thickness stability.Print provided by the invention can be used for calibration ellipsometer measurement range in the measurement capability of below 10nm.By evaluating the thickness evenness, thickness stability and uncertainty of print, the confidence level of print calibration result can be learnt.
Description
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to a value setting method and a preparation method of an ultrathin silicon dioxide film sample wafer.
Background
In the semiconductor field, the thickness of a film is an important parameter, and accurate measurement of the thickness parameter of the film is an important means for ensuring the quality of a device. The ellipsometer is mainly used for solving the problem of measuring the thickness of a thin film. To ensure the accuracy of the ellipsometer measurements, the instrument needs to be calibrated using standard coupons.
At present, as the feature size of devices produced in the microelectronic industry is reduced, the thin film becomes thinner and thinner, reaching below 10 nm. However, the lack of a standard wafer with a thin film thickness less than 10nm makes the ellipsometer unable to calibrate its measurement capability below 10 nm.
Disclosure of Invention
In view of this, the embodiment of the invention provides a method for determining the value of an ultrathin silica film sample and a preparation method thereof, so as to solve the problem that the measurement capability of an ellipsometer in the prior art is not calibrated within a measurement range of less than 10 nm.
The first aspect of the embodiment of the invention provides a value setting method for an ultrathin silicon dioxide film sample wafer, which comprises the following steps:
cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate;
growing a silicon dioxide film on the upper surface of the cleaned substrate through a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers;
selecting a value-selecting area on the silicon dioxide film, and selecting n measuring points in the value-selecting area;
measuring first thicknesses of the n measuring points by using a thickness measuring device, and determining the thickness uniformity of the sample wafer according to the first thicknesses;
measuring the second thicknesses of the n measuring points m times by using the thickness measuring device according to a preset time interval to obtain m thickness average values, and determining the thickness stability of the sample wafer according to the m thickness average values;
determining a component of uncertainty introduced by the thickness measurement device;
determining a synthetic uncertainty and an extended uncertainty of the sample wafer according to the uncertainty component, the thickness uniformity and the thickness stability;
wherein n and m are positive integers greater than 1.
Optionally, the synthetic uncertainty ucThe calculation formula of (2) is as follows:
the calculation formula of the expansion uncertainty U is as follows:
U＝2uc
wherein u is1An uncertainty component, u, introduced for said thickness measuring device2For thickness uniformity, u3For thickness stability.
Optionally, the measuring a first thickness of the n measuring points by using a thickness measuring device, and determining the thickness uniformity of the sample wafer according to the first thickness includes:
and measuring the first thicknesses of the n measuring points to obtain n first thickness values, and taking the difference between the maximum value and the minimum value of the n first thickness values as the thickness uniformity of the sample wafer.
Optionally, thickness stability u3The calculation formula of (2) is as follows:
wherein,the thickness average determined for the ith measurement,
optionally, the thickness measuring device is an ellipsometer;
the determining the uncertainty component introduced by the thickness measurement device comprises:
constructing a database of the corresponding relation between the thickness of the silicon dioxide film and the elliptical deflection angle and the phase difference;
repeatedly measuring the jth measuring point k times by using the thickness measuring device to obtain k groups of polarization angles and phase differences, and respectively constructing a normal distribution curve about the polarization angles and a normal distribution curve about the phase differences according to the k groups of polarization angles and the phase differences;
selecting h groups of first polarization angles and first phase differences from the normal distribution curve about the polarization angles and the normal distribution curve about the phase differences, matching the h groups of first polarization angles and the first phase differences with the database to obtain h third thicknesses, and calculating standard deviations of the third thicknesses, wherein the standard deviations of the third thicknesses are uncertainty components introduced by the thickness measuring device;
wherein h and k are positive integers greater than 1.
Further, the constructing a database of the corresponding relationship between the thickness of the silicon dioxide film and the elliptical deflection angle and the phase difference comprises:
constructing a structural model and a dispersion model; the structure model is a silicon substrate and a silicon dioxide film on the upper surface of the silicon substrate, and the dispersion parameter of the silicon dioxide, the dispersion parameter of the silicon, the wavelength of incident light and the incident angle are set;
constructing a function of the relation between the thickness of the silicon dioxide film and the polarization angle and phase difference according to the structure model and the dispersion model;
wherein, the function of the relation between the thickness of the silicon dioxide film and the polarization angle and the phase difference is obtained according to the following formula,
ρ is an elliptic function of the silicon dioxide film,is the amplitude reflection coefficient for the p-polarization direction,amplitude reflection coefficient, r, for the s-polarization directionpThe mode of the amplitude reflection coefficient, r, for the p-polarization directionsIs the mode of the amplitude reflection coefficient of the s-polarization direction,for the phase of the p-polarization,for s-polarization phase, Ψ is the polarization angle, Δ is the phase difference, r1sThe Fresnel reflection coefficient of s-direction polarization component of the interface of air and silicon dioxide film2sThe Fresnel reflection coefficient of the s-direction polarization component of the interface of the silicon dioxide film and the substrate is delta1Is the phase thickness of the film to be measured, n0Is refractive index of air, theta0Is an angle of incidence, n1Is the refractive index of the silica film, theta1Is the angle of incidence, n, in the silicon dioxide film2Is the refractive index of the substrate, θ2Is the angle of refraction, r, within the substrate1pFresnel reflection coefficient of p-direction polarization component of interface 1, r2pFresnel reflection coefficient of p-direction polarization component of interface 2, d1Is the thickness of the silicon dioxide film, lambda incident light wavelength;
and determining the corresponding relation between the silicon dioxide film with the thickness of 0 to 10 nanometers and the polarization angle and the phase difference according to the function.
Further, the selecting h sets of the first polarization angle and the first phase difference from the normal distribution curve about the polarization angle and the normal distribution curve about the phase difference, and matching with the database to obtain h third thicknesses includes:
selecting 1 first polarization angle from the normal distribution curve on the polarization angle, and selecting 1 first phase difference from the normal distribution curve on the phase difference;
calculating an evaluation function value of the first polarization angle and the first phase difference and each group of second polarization angles and second phase differences in the database by adopting a general search method, wherein the evaluation function of the first polarization angle and the first phase difference and the jth group of second polarization angles and second phase differences in the database is as follows:
is the value of the j-th merit function, ΨjFor the value of the j-th set of second polarization angles, Δ, in the databasejΨ values of the j-th set of second phase differences in the databaseexpFor a selected value of the first polarization angle, ΔexpIs the value of the selected first phase difference;
selecting the thickness of the silicon dioxide film corresponding to the second polarization angle and the second phase difference which enable the evaluation function value to be minimum as a third thickness;
and repeating the steps of selecting 1 first polarization angle from the normal distribution curve on the polarization angle and selecting 1 first phase difference from the normal distribution curve on the phase difference until h third thicknesses are obtained.
Optionally, cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate, including:
putting the substrate into a first cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the first cleaning solution is a mixed solution of distilled water, ammonia water and hydrogen peroxide, and the volume ratio of the distilled water to the ammonia water to the hydrogen peroxide is 4:1: 1;
washing the substrate to neutrality by using distilled water;
cleaning the substrate in a hydrofluoric acid solution for 2 to 5 minutes;
washing the substrate to neutrality by using distilled water;
putting the substrate into a second cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the second cleaning solution is a mixed solution of distilled water, hydrochloric acid and hydrogen peroxide, and the volume ratio of the distilled water to the hydrochloric acid to the hydrogen peroxide is 4:1: 1;
washing the substrate to neutrality by using distilled water;
the substrate was blow dried with nitrogen.
Optionally, the thickness of the silicon dioxide film is 2nm to 5 nm.
The second aspect of the embodiments of the present invention provides a method for preparing an ultrathin silica film sample wafer, including:
cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate;
and growing a silicon dioxide film on the upper surface of the cleaned substrate by a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers.
Compared with the prior art, the embodiment of the invention has the following beneficial effects: the ultrathin silicon dioxide film sample provided by the embodiment of the invention can be used for calibrating the measurement capability of an ellipsometer with the measurement range below 10 nm. The thickness uniformity of the sample wafer can be determined by measuring the first thickness of n measuring points in the constant value region by using the thickness measuring device, the thickness stability of the sample wafer can be determined by measuring the second thickness of n measuring points m times by using the thickness measuring device according to the preset time interval, the uncertainty component introduced by the thickness measuring device is determined, and finally the synthesis uncertainty and the expansion uncertainty of the sample wafer are determined according to the uncertainty component, the thickness uniformity and the thickness stability. By the method, the thickness uniformity, the thickness stability and the uncertainty of the sample wafer can be evaluated, so that the reliability of the sample wafer calibration result can be obtained.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic flow chart illustrating a method for setting a value of an ultra-thin silicon dioxide film sample wafer according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an ultra-thin silicon dioxide film sample wafer according to an embodiment of the present invention;
FIG. 3 is a thickness chart of an ultra-thin silicon dioxide film sample with a nominal thickness of 2nm according to an embodiment of the present invention;
FIG. 4 is a thickness chart of an ultra-thin silicon dioxide film sample wafer with a nominal thickness of 5nm according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a structural model according to an embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
Example one
Referring to fig. 1, a method for evaluating an ultra-thin silicon dioxide film sample includes:
step S101, cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate.
Optionally, the specific implementation manner of step S101 is: putting the substrate into a first cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the first cleaning solution is a mixed solution of distilled water, ammonia water and hydrogen peroxide, and the volume ratio of the distilled water to the ammonia water to the hydrogen peroxide is 4:1: 1; washing the substrate to neutrality by using distilled water; cleaning the substrate in a hydrofluoric acid solution for 2 to 5 minutes; washing the substrate to neutrality by using distilled water; putting the substrate into a second cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the second cleaning solution is a mixed solution of distilled water, hydrochloric acid and hydrogen peroxide, and the volume ratio of the distilled water to the hydrochloric acid to the hydrogen peroxide is 4:1: 1; washing the substrate to neutrality by using distilled water; the substrate was blow dried with nitrogen.
And S102, growing a silicon dioxide film on the upper surface of the cleaned substrate through a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers.
In the embodiment of the invention, the thickness of the silicon dioxide film grown by the rapid thermal oxidation process is controllable and has good uniformity. And controlling the growth temperature, the oxidation time and the oxygen content to obtain the silicon dioxide film with the required thickness. For example, when a silica film having a nominal thickness of 2nm is grown, the maximum temperature is 800 ℃, the oxidation time is 30 seconds, the oxygen content is 10%, and the other gas is argon. When a silicon dioxide film with the nominal thickness of 5 nanometers is grown, the highest temperature is 1000 ℃, the oxidation time is 90 seconds, the oxygen content is 10 percent, and the other gas is argon.
Optionally, the thickness of the silicon dioxide film is 2nm to 5nm
Step S103, selecting a value-fixed area on the silicon dioxide film, and selecting n measuring points in the value-fixed area. Wherein n is a positive integer greater than 1.
In the embodiment of the invention, a 4-inch silicon wafer is selected as the substrate, a constant value area is selected after a silicon dioxide film is grown on the upper surface of the silicon wafer, and n measuring points are selected in the constant value area. For example, as shown in fig. 2, a constant value region 202 is selected in a silica thin film sample 201, the constant value region 202 is a circle having a diameter of 10 mm, and 5 measurement points 203 are selected in the constant value region 202. The constant value area 202 can be located in the middle or near the edge of the silicon dioxide film sample 201, and the distribution of the measurement points 203 in the constant value area 202 is not limited.
And step S104, measuring the first thickness of the n measuring points by using a thickness measuring device, and determining the thickness uniformity of the sample wafer according to the first thickness.
Optionally, the specific implementation manner of step S104 is: and measuring the first thicknesses of the n measuring points to obtain n first thickness values, and taking the difference between the maximum value and the minimum value of the n first thickness values as the thickness uniformity of the sample wafer. Wherein n is a positive integer greater than 1.
In the embodiment of the present invention, the thickness measuring device is an ellipsometer, the number of the measuring points may be 5, the ellipsometer is used to measure the first thicknesses of the 5 measuring points respectively, so as to obtain 5 first thickness values, and the difference between the maximum value and the minimum value of the 5 first thickness values is used as the thickness uniformity of the sample. For example, as shown in Table 1, the thickness uniformity of a sample of a silica thin film having a nominal thickness of 2nm is 0.05 nm, and the thickness uniformity of a sample of a silica thin film having a nominal thickness of 5nm is 0.06 nm.
TABLE 1 thickness uniformity of the coupons
And S105, measuring the second thicknesses of the n measuring points m times by using the thickness measuring device according to a preset time interval to obtain m thickness average values, and determining the thickness stability of the sample wafer according to the m thickness average values. Wherein n and m are positive integers greater than 1.
Optionally, thickness stability u3The calculation formula of (2) is as follows:
wherein,the thickness average determined for the ith measurement;
in the embodiment of the invention, the thickness stability reflects the change rule of the thickness of the silicon dioxide film along with the time. For example, 5 measurement points are selected, the second thickness of the 5 measurement points is measured every month for 12 times, the average value of the second thickness of the 5 measurement points measured in the ith time is calculated according to the formula (2), and finally the stability of the thickness is calculated according to the formula (1).
Wherein d isjIs the thickness of the jth measurement point in the ith measurement.
Fig. 3 is a time-dependent change law of the average thickness of 5 measurement points of a silica film sample wafer with a nominal thickness of 2nm, and the thickness stability is 0.05 nm, and fig. 4 is a time-dependent change law of the average thickness of 5 measurement points of a silica film sample wafer with a nominal thickness of 5nm, and the thickness stability is 0.05 nm.
And step S106, determining an uncertainty component introduced by the thickness measuring device.
Optionally, the thickness measuring device is an ellipsometer. The specific implementation manner of step S106 is: the determining the uncertainty component introduced by the thickness measurement device comprises:
constructing a database of the corresponding relation between the thickness of the silicon dioxide film and the elliptical deflection angle and the phase difference;
repeatedly measuring the jth measuring point k times by using the thickness measuring device to obtain k groups of polarization angles and phase differences, and respectively constructing a normal distribution curve about the polarization angles and a normal distribution curve about the phase differences according to the k groups of polarization angles and the phase differences;
selecting h groups of first polarization angles and first phase differences from the normal distribution curve about the polarization angles and the normal distribution curve about the phase differences, matching the h groups of first polarization angles and the first phase differences with the database to obtain h third thicknesses, and calculating standard deviations of the third thicknesses, wherein the standard deviations of the third thicknesses are uncertainty components introduced by the thickness measuring device;
wherein h and k are positive integers greater than 1.
Further, the constructing a database of the corresponding relationship between the thickness of the silicon dioxide film and the elliptical deflection angle and the phase difference comprises:
constructing a structural model and a dispersion model; the structure model is a silicon substrate and a silicon dioxide film on the upper surface of the silicon substrate, and the dispersion parameter of the silicon dioxide, the dispersion parameter of the silicon, the wavelength of incident light and the incident angle are set;
constructing a function of the relation between the thickness of the silicon dioxide film and the polarization angle and phase difference according to the structure model and the dispersion model;
wherein, the function of the relation between the thickness of the silicon dioxide film and the polarization angle and the phase difference is obtained according to the following formula,
ρ is an elliptic function of the silicon dioxide film,is the amplitude reflection coefficient for the p-polarization direction,amplitude reflection coefficient, r, for the s-polarization directionpThe mode of the amplitude reflection coefficient, r, for the p-polarization directionsIs the mode of the amplitude reflection coefficient of the s-polarization direction,for the phase of the p-polarization,is s-polarized phaseΨ is the angle of polarization, Δ is the phase difference, r1sThe Fresnel reflection coefficient of s-direction polarization component of the interface of air and silicon dioxide film2sThe Fresnel reflection coefficient of the s-direction polarization component of the interface of the silicon dioxide film and the substrate is delta1Is the phase thickness of the film to be measured, n0Is refractive index of air, theta0Is an angle of incidence, n1Is the refractive index of the silica film, theta1Is the angle of incidence, n, in the silicon dioxide film2Is the refractive index of the substrate, θ2Is the angle of refraction, r, within the substrate1pFresnel reflection coefficient of p-direction polarization component of interface 1, r2pFresnel reflection coefficient of p-direction polarization component of interface 2, d1Is the thickness of the silicon dioxide film, lambda incident light wavelength;
and determining the corresponding relation between the silicon dioxide film with the thickness of 0 to 10 nanometers and the polarization angle and the phase difference according to the function.
In the embodiment of the present invention, the structural model is shown in fig. 5, and the structural model includes a silicon substrate 501 and a silicon dioxide film 502 on the upper surface of the silicon substrate. The dispersion model is the dispersion parameter of silicon and silicon dioxide, wherein the dispersion parameter of silicon dioxide is n11.46, the dispersion parameter of silicon is n2＝3.875-0.016i，n1Is the refractive index of the silica film, n2Is the substrate index of refraction. The incident wavelength is selected from the commonly used wavelength λ of 632.8nm, the incident angle is an angle suitable for the spectroscopic ellipsometer, and the incident angle θ in this embodiment is065 deg. is obtained. The functions of the thickness of the silica film as a function of the polarization angle and the phase difference can be obtained from the equations (3) to (6), i.e.
f(d1)＝tanΨejΔ(7)
According to the formula (7), the thickness of the silica film corresponds to the polarization angle and the phase difference one by one, and after the thickness of the silica film is determined, a unique set of the polarization angle and the phase difference can be obtained. According to the formula (7), determining the corresponding relation between the silicon dioxide film with the thickness of 0-10 nanometers and the polarization angle and the phase difference, and obtaining a database of the corresponding relation between the silicon dioxide film thickness and the elliptical deflection angle and the phase difference, wherein the thickness interval is 0.02 nanometers.
Further, the selecting h sets of the first polarization angle and the first phase difference from the normal distribution curve about the polarization angle and the normal distribution curve about the phase difference, and matching with the database to obtain h third thicknesses includes:
selecting 1 first polarization angle from the normal distribution curve on the polarization angle, and selecting 1 first phase difference from the normal distribution curve on the phase difference;
calculating an evaluation function value of the first polarization angle and the first phase difference and each group of second polarization angles and second phase differences in the database by adopting a general search method, wherein the evaluation function of the first polarization angle and the first phase difference and the jth group of second polarization angles and second phase differences in the database is as follows:
is the value of the j-th merit function, ΨjFor the value of the j-th set of second polarization angles, Δ, in the databasejΨ values of the j-th set of second phase differences in the databaseexpFor a selected value of the first polarization angle, ΔexpIs the value of the selected first phase difference;
selecting the thickness of the silicon dioxide film corresponding to the second polarization angle and the second phase difference which enable the evaluation function value to be minimum as a third thickness;
and repeating the steps of selecting 1 first polarization angle from the normal distribution curve on the polarization angle and selecting 1 first phase difference from the normal distribution curve on the phase difference until h third thicknesses are obtained.
In the embodiment of the present invention, the j-th measurement point is repeatedly measured k times by using a spectroscopic ellipsometer, k sets of polarization angles and phase differences are obtained, expected values and standard deviations of the polarization angles and the phase differences are calculated, respectively, and a normal distribution curve with respect to the polarization angles and a normal distribution curve with respect to the phase differences are constructed. For example, the jth measurement point is measured 6 times using a spectroscopic ellipsometer, 6 sets of polarization angles and phase differences are obtained, expected values and variances of the phase differences and the polarization angles are calculated, respectively, and a normal distribution curve with respect to the polarization angles and a normal distribution curve with respect to the phase differences are constructed. Table 2 shows the expected values and the variances of the polarization angles and the phase differences of the silica film samples having a nominal thickness of 2nm and the silica film samples having a nominal thickness of 5 nm.
TABLE 2 expected values and standard deviations
The measurement uncertainty of the spectroscopic ellipsometer was assessed using the MCM method (monte carlo method). Randomly selecting 1 first polarization angle psi from normal distribution curve of polarization angleexpRandomly selecting 1 first phase difference Delta from a normal distribution curve of phase differencesexpTo obtain a set of (Ψ)exp，Δexp) Will (Ψ)exp，Δexp) And in the database (Ψ)j，Δj) Matching, wherein j is 1, 2, 3, …, l, and the matching method is as follows: calculating (Ψ) according to the merit function (6)exp，Δexp) And (Ψ) in the databasej，Δj) Will minimize the evaluation function value (Ψ) toj，Δj) The corresponding thickness is used as a third thickness, and the repeated steps randomly select 1 first polarization angle psi from the normal distribution curve of the polarization anglesexpUntil h third thicknesses are obtained. For example, when h is 10000, a spectroscopic ellipsometer for a silica thin film sample with a nominal thickness of 2nm introduces an uncertainty component of 0.04 nm and a spectroscopic ellipsometer for a silica thin film sample with a nominal thickness of 5nmThe bias meter introduced an uncertainty component of 0.04 nm.
And S107, determining the synthesis uncertainty and the expansion uncertainty of the sample wafer according to the uncertainty component, the thickness uniformity and the thickness stability.
Optionally, the synthetic uncertainty ucThe calculation formula of (2) is as follows:
the formula for calculating the extended uncertainty U is:
U＝2uc(10)
u1component of uncertainty, u, introduced for said spectroscopic ellipsometer2For thickness uniformity, u3For thickness stability.
In an embodiment of the invention, the uncertainty component u is introduced from a spectroscopic ellipsometer1Thickness uniformity u2And thickness stability u3The synthesis uncertainty component and the extension uncertainty component were calculated, and Table 3 shows the uncertainty of the silica thin film sample having a nominal thickness of 2nm and the silica thin film sample having a nominal thickness of 5 nm. It can be seen that the uncertainty of the silicon dioxide film sample with the nominal thickness of 2nm and the silicon dioxide film sample with the nominal thickness of 5nm is very small, which indicates that the reliability of the measurement result is very high.
TABLE 3 uncertainty
| Nominal thickness | u1 | u2 | u3 | Synthetic uncertainty | Extended uncertainty |
| 2nm | 0.05nm | 0.05nm | 0.05nm | 0.09nm | 0.18nm |
| 5nm | 0.06nm | 0.06nm | 0.05nm | 0.10nm | 0.20nm |
The ultrathin silicon dioxide film sample provided by the embodiment of the invention can be used for calibrating the measurement capability of an ellipsometer with the measurement range below 10 nm. The thickness uniformity of the sample wafer can be determined by measuring the first thickness of n measuring points in the constant value region by using the thickness measuring device, the thickness stability of the sample wafer can be determined by measuring the second thickness of n measuring points m times by using the thickness measuring device according to the preset time interval, the uncertainty component introduced by the thickness measuring device is determined, and finally the synthesis uncertainty and the expansion uncertainty of the sample wafer are determined according to the uncertainty component, the thickness uniformity and the thickness stability. By the method, the thickness uniformity, the thickness stability and the uncertainty of the sample wafer can be evaluated, so that the reliability of the sample wafer calibration result can be obtained.
Example two
A preparation method of an ultrathin silicon dioxide film sample wafer comprises the following steps:
cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate;
and growing a silicon dioxide film on the upper surface of the cleaned substrate by a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers.
In the embodiment of the invention, the substrate is put into a first cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the first cleaning solution is a mixed solution of distilled water, ammonia water and hydrogen peroxide, and the volume ratio of the distilled water to the ammonia water to the hydrogen peroxide is 4:1: 1; washing the substrate to neutrality by using distilled water; cleaning the substrate in a hydrofluoric acid solution for 2 to 5 minutes; washing the substrate to neutrality by using distilled water; putting the substrate into a second cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the second cleaning solution is a mixed solution of distilled water, hydrochloric acid and hydrogen peroxide, and the volume ratio of the distilled water to the hydrochloric acid to the hydrogen peroxide is 4:1: 1; washing the substrate to neutrality by using distilled water; the substrate was blow dried with nitrogen.
The silicon dioxide film grown by the rapid thermal oxidation process has controllable thickness and good uniformity. And controlling the growth temperature, the oxidation time and the oxygen content to obtain the silicon dioxide film with the required thickness. For example, when a silica film having a nominal thickness of 2nm is grown, the maximum temperature is 800 ℃, the oxidation time is 30 seconds, the oxygen content is 10%, and the other gas is argon. When a silicon dioxide film with the nominal thickness of 5 nanometers is grown, the highest temperature is 1000 ℃, the oxidation time is 90 seconds, the oxygen content is 10 percent, and the other gas is argon.
According to the embodiment of the invention, the silicon dioxide film grows on the cleaned substrate through the rapid thermal oxidation process, and the silicon dioxide film has controllable thickness and good uniformity.
It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.
Claims (10)
1. A method for setting a value of an ultrathin silicon dioxide film sample wafer is characterized by comprising the following steps:
cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate;
growing a silicon dioxide film on the upper surface of the cleaned substrate through a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers;
selecting a value-selecting area on the silicon dioxide film, and selecting n measuring points in the value-selecting area;
measuring first thicknesses of the n measuring points by using a thickness measuring device, and determining the thickness uniformity of the sample wafer according to the first thicknesses;
measuring the second thicknesses of the n measuring points m times by using the thickness measuring device according to a preset time interval to obtain m thickness average values, and determining the thickness stability of the sample wafer according to the m thickness average values;
determining a component of uncertainty introduced by the thickness measurement device;
determining a synthetic uncertainty and an extended uncertainty of the sample wafer according to the uncertainty component, the thickness uniformity and the thickness stability;
wherein n and m are positive integers greater than 1.
2. The method of valuing an ultra-thin silica film sample as recited in claim 1 wherein the synthetic uncertainty u iscThe calculation formula of (2) is as follows:
the calculation formula of the expansion uncertainty U is as follows:
U＝2uc
wherein u is1An uncertainty component, u, introduced for said thickness measuring device2For thickness uniformity, u3For thickness stability.
3. The method for valuing the ultra-thin silica film sample wafer as claimed in claim 1, wherein the step of measuring a first thickness of n measurement points by using a thickness measuring device, and the step of determining the thickness uniformity of the sample wafer according to the first thickness comprises the steps of:
and measuring the first thicknesses of the n measuring points to obtain n first thickness values, and taking the difference between the maximum value and the minimum value of the n first thickness values as the thickness uniformity of the sample wafer.
4. A method for evaluating a value of an ultra-thin silica film sample as recited in claim 1, wherein the thickness stability u is3The calculation formula of (2) is as follows:
wherein,the thickness average determined for the ith measurement,
5. a method for valuing an ultra-thin silica film sample according to claim 1, wherein the thickness measuring device is an ellipsometer;
the determining the uncertainty component introduced by the thickness measurement device comprises:
constructing a database of the corresponding relation between the thickness of the silicon dioxide film and the elliptical deflection angle and the phase difference;
repeatedly measuring the jth measuring point k times by using the thickness measuring device to obtain k groups of polarization angles and phase differences, and respectively constructing a normal distribution curve about the polarization angles and a normal distribution curve about the phase differences according to the k groups of polarization angles and the phase differences;
h groups of first polarization angles and first phase differences are selected from the normal distribution curve about the polarization angles and the normal distribution curve about the phase differences, h third thicknesses are obtained by matching the h groups of first polarization angles and the first phase differences with the database, and the standard deviation of the third thicknesses is calculated to be used as the uncertainty component introduced by the thickness measuring device;
wherein h and k are positive integers greater than 1.
6. The method for valuing the ultrathin silica film sample wafer as claimed in claim 5, wherein the step of constructing a database of the corresponding relation between the thickness of the silica film and the elliptical deflection angle and the phase difference comprises the following steps:
constructing a structural model and a dispersion model; the structure model is a silicon substrate and a silicon dioxide film on the upper surface of the silicon substrate, and the dispersion parameter of the silicon dioxide, the dispersion parameter of the silicon, the wavelength of incident light and the incident angle are set;
constructing a function of the relation between the thickness of the silicon dioxide film and the polarization angle and phase difference according to the structure model and the dispersion model;
wherein, the function of the relation between the thickness of the silicon dioxide film and the polarization angle and the phase difference is obtained according to the following formula,
ρ is an elliptic function of the silicon dioxide film,is the amplitude reflection coefficient for the p-polarization direction,amplitude reflection coefficient, r, for the s-polarization directionpThe mode of the amplitude reflection coefficient, r, for the p-polarization directionsIs the mode of the amplitude reflection coefficient of the s-polarization direction,for the phase of the p-polarization,for s-polarization phase, Ψ is the polarization angle, Δ is the phase difference, r1sThe Fresnel reflection coefficient of s-direction polarization component of the interface of air and silicon dioxide film2sThe Fresnel reflection coefficient of the s-direction polarization component of the interface of the silicon dioxide film and the substrate is delta1Is the phase thickness of the film to be measured, n0Is refractive index of air, theta0Is an angle of incidence, n1Is the refractive index of the silica film, theta1Is the angle of incidence, n, in the silicon dioxide film2Is the refractive index of the substrate, θ2Is the angle of refraction, r, within the substrate1pFresnel reflection coefficient of p-direction polarization component of interface 1, r2pFresnel reflection coefficient of p-direction polarization component of interface 2, d1Is the thickness of the silicon dioxide film, lambda incident light wavelength;
and determining the corresponding relation between the silicon dioxide film with the thickness of 0 to 10 nanometers and the polarization angle and the phase difference according to the function.
7. The method for valuing the ultrathin silica film sample as claimed in claim 5, wherein the step of selecting h groups of the first polarization angle and the first phase difference from the normal distribution curve about the polarization angle and the normal distribution curve about the phase difference and matching the h groups of the first polarization angle and the first phase difference with the database to obtain h third thicknesses comprises the steps of:
selecting 1 first polarization angle from the normal distribution curve on the polarization angle, and selecting 1 first phase difference from the normal distribution curve on the phase difference;
calculating an evaluation function value of the first polarization angle and the first phase difference and each group of second polarization angles and second phase differences in the database by adopting a general search method, wherein the evaluation function of the first polarization angle and the first phase difference and the jth group of second polarization angles and second phase differences in the database is as follows:
is the value of the j-th merit function, ΨjFor the value of the j-th set of second polarization angles, Δ, in the databasejΨ values of the j-th set of second phase differences in the databaseexpFor a selected value of the first polarization angle, ΔexpIs the value of the selected first phase difference;
selecting the thickness of the silicon dioxide film corresponding to the second polarization angle and the second phase difference which enable the evaluation function value to be minimum as a third thickness;
and repeating the steps of selecting 1 first polarization angle from the normal distribution curve on the polarization angle and selecting 1 first phase difference from the normal distribution curve on the phase difference until h third thicknesses are obtained.
8. The method for valuing the ultrathin silicon dioxide film sample wafer as claimed in claim 1, wherein the step of cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate comprises the following steps:
putting the substrate into a first cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the first cleaning solution is a mixed solution of distilled water, ammonia water and hydrogen peroxide, and the volume ratio of the distilled water to the ammonia water to the hydrogen peroxide is 4:1: 1;
washing the substrate to neutrality by using distilled water;
cleaning the substrate in a hydrofluoric acid solution for 2 to 5 minutes;
washing the substrate to neutrality by using distilled water;
putting the substrate into a second cleaning solution with the temperature of 80-90 ℃ for cleaning for 10-15 minutes; the second cleaning solution is a mixed solution of distilled water, hydrochloric acid and hydrogen peroxide, and the volume ratio of the distilled water to the hydrochloric acid to the hydrogen peroxide is 4:1: 1;
washing the substrate to neutrality by using distilled water;
the substrate was blow dried with nitrogen.
9. The method for valuing an ultrathin silica film sample as claimed in any one of claims 1 to 8, wherein the thickness of the silica film is 2nm to 5 nm.
10. A preparation method of an ultrathin silicon dioxide film sample wafer is characterized by comprising the following steps:
cleaning the substrate in a cleaning solution to remove impurities on the surface of the substrate;
and growing a silicon dioxide film on the upper surface of the cleaned substrate by a rapid thermal oxidation process, wherein the thickness of the silicon dioxide film is less than 10 nanometers.
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