A method for measuring nitrogen concentration of silicon carbide wafer

Abstract

This invention relates to the field of silicon carbide technology and discloses a method for measuring the nitrogen concentration of a silicon carbide wafer, which involves calculating the first contact potential φ on the surface of the silicon carbide wafer. sample Then, by establishing the first contact potential φ sample The difference between the conduction band bottom energy Ec and the Fermi level energy Ef of a silicon carbide wafer is obtained by establishing the first relationship between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef. The specific value of the electron concentration n at equilibrium is then obtained by establishing the second relationship between the electron concentration n at equilibrium and the nitrogen concentration N. D The third relation yields the specific value of the nitrogen concentration n in the silicon carbide wafer; this allows the nitrogen content of silicon carbide to be obtained through surface potential testing, facilitating the production process and improving testing efficiency.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide technology, specifically to a method for measuring the nitrogen concentration of silicon carbide wafers. Background Technology

[0002] Currently, the commonly used method for testing impurity concentration in silicon carbide is secondary ion mass spectrometry (SIMS). This involves bombarding the surface of a silicon carbide wafer with a high-energy primary ion beam, causing sputtering and generating secondary particles. Analyzing these secondary ions reveals the elemental information of the silicon carbide wafer. However, SIMS testing has limitations. For example, it is destructive to the silicon carbide wafer and requires a strict testing environment, which must be performed under vacuum. In actual production, the nitrogen concentration of silicon carbide wafers is crucial for quality control. If an engineer needs to know the nitrogen concentration of a specific silicon carbide wafer at a particular stage of the process, using SIMS testing would damage the wafer surface, be time-consuming and labor-intensive, and could even affect the entire process schedule. Therefore, finding a method that can solve these problems and rapidly obtain nitrogen concentration is of paramount importance. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of existing nitrogen concentration measurement methods causing damage to the surface of silicon carbide wafers, being time-consuming and labor-intensive, and even affecting the progress of the entire process, and to provide a method for measuring the nitrogen concentration of silicon carbide wafers.

[0004] To achieve the above objectives, the present invention provides a method for measuring the nitrogen concentration of a silicon carbide wafer, comprising the following steps:

[0005] A silicon carbide wafer after electrostatic removal treatment is provided, and the first contact potential φ on the surface of the silicon carbide wafer is calculated. sample ;

[0006] Establish the first contact potential φ sample The first relationship between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer is given, based on the established first relationship and the first contact potential φ. sample The specific values ​​are calculated to obtain the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer;

[0007] A second relationship is established between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer and the electron concentration n of the silicon carbide wafer at equilibrium. Based on the second relationship and the difference between the conduction band bottom energy Ec and the Fermi level energy Ef, the specific value of the electron concentration n of the silicon carbide wafer at equilibrium is obtained.

[0008] Establish the electron concentration n corresponding to the nitrogen concentration N of a silicon carbide wafer at equilibrium. DThe third relation is used to obtain the specific value of the nitrogen concentration n of the silicon carbide wafer at equilibrium.

[0009] As one possible implementation, a silicon carbide wafer after electrostatic removal treatment is provided, and the first contact potential φ on the surface of the silicon carbide wafer is calculated. sample The specific steps include:

[0010] Provides silicon carbide wafers after electrostatic removal treatment and provides gold samples with known work functions;

[0011] The silicon carbide wafer and the gold sample were scanned using a microscope, and the first contact potential difference Δφ1 between the surface of the silicon carbide wafer and the probe of the microscope, and the second contact potential difference Δφ2 between the surface of the gold sample and the probe of the microscope were measured.

[0012] The first contact potential φ on the surface of the silicon carbide wafer is calculated based on the first contact potential difference Δφ1, the second contact potential difference Δφ2, and the work function of the gold sample. sample .

[0013] As one possible implementation, the first contact potential φ on the surface of the silicon carbide wafer is calculated based on the first contact potential difference Δφ1, the second contact potential difference Δφ2, and the work function of the gold sample. sample The calculation process specifically includes:

[0014] The first contact potential difference Δφ1=φ tip -φ sample In the formula, φ tip φ represents the potential of the probe surface. sample This represents the first contact potential on the surface of the silicon carbide wafer;

[0015] The second contact potential difference Δφ2=φ tip -φ metal In the formula, φ tip φ represents the potential of the probe surface. metal This represents the second contact potential on the surface of the gold sample;

[0016] Among them, due to Δφ1, Δφ2, φ metal Given that the first contact potential φ on the surface of the silicon carbide wafer is obtained, sample =Δφ2-Δφ1+φ metal .

[0017] As one possible implementation method, a first contact potential φ is established. sampleThe steps corresponding to the first relationship between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer specifically include: establishing the first contact potential φ sample The first relationship between the electron affinity energy x1, the conduction band bottom energy Ec, and the Fermi level energy Ef of the silicon carbide wafer;

[0018] The first relation is: φ sample =x1+Ec-Ef, where Ec-Ef represents the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer, and x1 represents the electron affinity.

[0019] As one possible implementation, the step of establishing a second relationship between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer and the electron concentration n of the silicon carbide wafer at equilibrium specifically includes:

[0020] The following parameters are established: the difference between the conduction band bottom energy Ec and the Fermi level energy Ef; the room temperature T at which the silicon carbide wafer is located; the Boltzmann constant k corresponding to the silicon carbide wafer; and the effective density of states N in the conduction band of the silicon carbide wafer. c The second relationship corresponding to the electron concentration n of the silicon carbide wafer at equilibrium.

[0021] The second relationship is: the electron concentration of the silicon carbide wafer at equilibrium. In the formula, N c The value represents the effective density of states in the conduction band of the silicon carbide wafer, k represents the Boltzmann constant corresponding to the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0022] As one possible implementation, the effective state density N in the conduction band of the silicon carbide wafer... c The calculation formula is:

[0023] In the formula, M represents the equivalent number of valleys in the conduction band of the silicon carbide wafer, m c It is the effective mass of a trough state density in the conduction band of the silicon carbide wafer, m o The value represents the electron mass in free space of the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0024] As one possible implementation method, the third relation is:

[0025]

[0026] In the formula, N c N represents the effective state density within the conduction band of the silicon carbide wafer. D E represents the nitrogen concentration of the silicon carbide wafer. c -ED The ionization energy of nitrogen is expressed in g. D The donor's degeneracy factor is represented, k represents the Boltzmann constant corresponding to the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0027] As one possible implementation, the steps of providing a silicon carbide wafer after electrostatic removal treatment specifically include: providing a silicon carbide wafer to be tested; immersing the silicon carbide wafer in a hydrofluoric acid solution to remove the oxide layer on the surface of the silicon carbide wafer; then washing away the residual hydrofluoric acid on the surface of the silicon carbide wafer with distilled water; and then using an electrostatic gun or an ion fan to perform air sweeping to remove surface static electricity from the surface of the silicon carbide wafer, thereby obtaining a silicon carbide wafer after electrostatic removal treatment.

[0028] As one possible implementation, the first contact potential difference Δφ1 between the silicon carbide wafer surface and the microscope probe, and the second contact potential difference Δφ2 between the gold sample surface and the microscope probe, are both measured by randomly selecting a scanning area of ​​the silicon carbide wafer surface and the gold sample surface, respectively.

[0029] Beneficial effects of the present invention: The present invention discloses a method for measuring the nitrogen concentration of a silicon carbide wafer, which is achieved by calculating the first contact potential φ on the surface of the silicon carbide wafer. sample Then, by establishing the first contact potential φ sample The difference between the conduction band bottom energy Ec and the Fermi level energy Ef of a silicon carbide wafer is obtained by establishing a first relationship between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef. The specific value of the electron concentration n at equilibrium is then obtained by establishing a second relationship between the electron concentration n at equilibrium and the nitrogen concentration N. D The third relation yields the specific value of the nitrogen concentration n in the silicon carbide wafer; this allows the nitrogen content of silicon carbide to be obtained through surface potential testing, facilitating the production process and improving testing efficiency. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the steps of a method for calculating the nitrogen concentration of a silicon carbide wafer according to an embodiment of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] See Figure 1 This embodiment provides a technical solution: a method for measuring the nitrogen concentration of a silicon carbide wafer, characterized by comprising the following steps:

[0033] Step S100: Provide a silicon carbide wafer after electrostatic removal treatment, and calculate the first contact potential φ on the surface of the silicon carbide wafer. sample ;

[0034] Step S200: Establish the first contact potential φ sample The first relationship between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer is given, based on the established first relationship and the first contact potential φ. sample The specific values ​​are calculated to obtain the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer;

[0035] Step S300: Establish a second relationship between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer and the electron concentration n of the silicon carbide wafer at equilibrium. Based on the second relationship and the difference between the conduction band bottom energy Ec and the Fermi level energy Ef, obtain the specific value of the electron concentration n of the silicon carbide wafer at equilibrium.

[0036] Step S400: Establish the nitrogen concentration N corresponding to the electron concentration n of the silicon carbide wafer at equilibrium. D The third relation is used to obtain the specific value of the nitrogen concentration n of the silicon carbide wafer at equilibrium.

[0037] The specific steps of performing step S100, which provides a silicon carbide wafer after electrostatic removal treatment, include: providing a silicon carbide wafer to be tested; immersing the silicon carbide wafer in a hydrofluoric acid solution to remove the oxide layer on the surface of the silicon carbide wafer; then washing away the residual hydrofluoric acid on the surface of the silicon carbide wafer with distilled water; and then using an electrostatic gun or an ion fan to air-sweep the surface of the silicon carbide wafer to remove surface static electricity, thereby obtaining a silicon carbide wafer after electrostatic removal treatment.

[0038] Specifically, immersing the silicon carbide wafer in a hydrofluoric acid solution includes immersing the silicon carbide wafer in a 5% hydrofluoric acid solution for 10 minutes.

[0039] A silicon carbide wafer after electrostatic removal treatment is provided, and the first contact potential φ on the surface of the silicon carbide wafer is calculated. sample The specific steps include:

[0040] Provides silicon carbide wafers after electrostatic removal treatment and provides gold samples with known work functions;

[0041] The silicon carbide wafer and the gold sample were scanned using a microscope, and the first contact potential difference Δφ1 between the surface of the silicon carbide wafer and the probe of the microscope, and the second contact potential difference Δφ2 between the surface of the gold sample and the probe of the microscope were measured.

[0042] The first contact potential φ on the surface of the silicon carbide wafer is calculated based on the first contact potential difference Δφ1, the second contact potential difference Δφ2, and the work function of the gold sample. sample .

[0043] In this embodiment, the microscope used is an atomic force microscope, and the Kelvin probe microscope mode is selected. The gold sample can be copper.

[0044] The first contact potential difference Δφ1 between the silicon carbide wafer surface and the microscope probe, and the second contact potential difference Δφ2 between the gold sample surface and the microscope probe, are both measured by randomly selecting a scanning area of ​​the silicon carbide wafer surface and the gold sample surface, respectively.

[0045] Specifically, the microscope randomly selects a point on the surface of the silicon carbide wafer, scans a 5μm×5μm area, and then uses analysis software such as Nanoscop Analysis to obtain the first contact potential difference Δφ1 between the probe and the surface of the silicon carbide wafer; similarly, the microscope is used to obtain the second contact potential difference Δφ2 between the surface of the gold sample and the probe of the microscope.

[0046] The first contact potential φ on the surface of the silicon carbide wafer is calculated based on the first contact potential difference Δφ1, the second contact potential difference Δφ2, and the work function of the gold sample. sample The calculation process specifically includes:

[0047] The first contact potential difference Δφ1=φ tip -φ sample In the formula, φ tip φ represents the potential of the probe surface. sample This represents the first contact potential on the surface of the silicon carbide wafer;

[0048] The second contact potential difference Δφ2=φ tip -φ metal In the formula, φ tip φ represents the potential of the probe surface. metal This represents the second contact potential on the surface of the gold sample;

[0049] Among them, due to φ metal It is obtained from the work function of the gold standard sample, i.e., φ metalThe numerical values ​​of Δφ1 and the gold standard sample are the same, the difference lies in the units. For example, the unit of Δφ1 is volts (V), and φ... metal The unit is electron volt (eV), therefore φ metal Since Δφ1 and Δφ2 have been calculated, the first contact potential φ on the surface of the silicon carbide wafer can be obtained. sample =Δφ2-Δφ1+φ metal .

[0050] In other embodiments, instead of using a gold standard sample, calibration can be performed using highly oriented pyrolytic graphite (HOPG).

[0051] Execute step S200 to establish the first contact potential φ sample The steps corresponding to the first relationship between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer specifically include: establishing the first contact potential φ sample The first relationship between the electron affinity energy x1, the conduction band bottom energy Ec, and the Fermi level energy Ef of the silicon carbide wafer;

[0052] The first relation is: φ sample =x1+Ec-Ef, where Ec-Ef represents the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer, and x1 represents the electron affinity.

[0053] Generally, the electron affinity x1 of a 4H-type silicon carbide wafer is 3.8, thus the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer can be obtained as Ec-Ef.

[0054] Step S300, establishing the second relationship between the difference between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer and the electron concentration n of the silicon carbide wafer at equilibrium, specifically includes:

[0055] The following parameters are established: the difference between the conduction band bottom energy Ec and the Fermi level energy Ef; the room temperature T at which the silicon carbide wafer is located; the Boltzmann constant k corresponding to the silicon carbide wafer; and the effective density of states N in the conduction band of the silicon carbide wafer. c The second relationship corresponding to the electron concentration n of the silicon carbide wafer at equilibrium.

[0056] The second relationship is: the electron concentration of the silicon carbide wafer at equilibrium. In the formula, N c The value represents the effective density of states in the conduction band of the silicon carbide wafer, k represents the Boltzmann constant corresponding to the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0057] Furthermore, as one embodiment, the effective state density N in the conduction band of the silicon carbide wafer... c The calculation formula is:

[0058] The effective state density within the conduction band of the silicon carbide wafer In the formula, M represents the equivalent number of valleys in the conduction band of the silicon carbide wafer, m c It is the effective mass of a trough state density in the conduction band of the silicon carbide wafer, m o The value represents the electron mass in free space of the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0059] Since silicon carbide is at room temperature, T is taken as 300, and M represents the equivalent number of valleys in the conduction band of the silicon carbide wafer, which is generally taken as 3. Therefore, substituting the value into the formula yields N. C =1.69x10 19 .

[0060] The effective state density N in the conduction band of the silicon carbide wafer was calculated. c After obtaining the specific values, substitute them into the second relationship, and the difference E between the conduction band bottom energy Ec and the Fermi level energy Ef of the silicon carbide wafer... c -E f Since the value of k is known (the Boltzmann constant is also known), and T is 300, the specific value of the electron concentration n of the silicon carbide wafer at equilibrium can be obtained.

[0061] Execute step S400, the third relation is:

[0062]

[0063] In the formula, N c N represents the effective state density within the conduction band of the silicon carbide wafer. D E represents the nitrogen concentration of the silicon carbide wafer. c -E D The ionization energy of nitrogen is expressed in g. D The donor's degeneracy factor is represented, k represents the Boltzmann constant corresponding to the silicon carbide wafer, and T represents the room temperature at which the silicon carbide wafer is located.

[0064] Among them, E c -E D That is, the ionization energy of nitrogen is 61.4 meV, k is the Boltzmann constant which is also known, T is taken as the room temperature of the silicon carbide wafer, 300, and g D The donor's degeneracy factor, usually taken as 2, is substituted into the third relational expression along with the specific value of the electron concentration n of the silicon carbide wafer at equilibrium, thereby calculating the specific value of the nitrogen concentration of the silicon carbide wafer.

[0065] This invention uses atomic force microscopy to test the surface potential of silicon carbide wafers. By analyzing the relationship between surface potential and nitrogen content in silicon carbide, the nitrogen content of silicon carbide can be obtained from the surface potential test results, which provides convenience for the production process and improves testing efficiency.

[0066] In addition, atomic force microscopy can also perform morphology testing. The surface roughness value obtained from morphology testing is a necessary indicator for the shipment of silicon carbide products. After chemical mechanical polishing, the surface roughness is tested by atomic force microscopy. When the surface roughness Ra≤0.2nm, it meets the shipment standard.

[0067] This invention relates to a novel method for measuring nitrogen concentration in silicon carbide. Compared to the traditional SIMS method for measuring nitrogen concentration, this invention is simple to operate and requires no new testing equipment. The test results can be obtained using only an atomic force microscope. Furthermore, the surface roughness value and surface contact potential difference of the sample can be obtained simultaneously using a Kelvin probe microscope, making it even more convenient.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method of measuring the nitrogen concentration of a silicon carbide wafer, comprising: Includes the following steps: A silicon carbide wafer after electrostatic removal treatment is provided, and a first contact potential of a surface of the silicon carbide wafer is measured ; Establishing the first contact potential The corresponding conduction band bottom energy Ec and Fermi level energy of the silicon carbide wafer The first relation, based on the established first relation and the first contact potential The specific value was calculated to obtain the conduction band bottom energy of the silicon carbide wafer. and Fermi level energy The difference; Establish the conduction band bottom energy of the silicon carbide wafer. and Fermi level energy The difference corresponds to the electron concentration of the silicon carbide wafer at equilibrium. The second relation, based on the second relation and the conduction band bottom energy and Fermi level energy The difference is used to obtain the electron concentration of the silicon carbide wafer at equilibrium. The specific value; Establish the electron concentration of silicon carbide wafers at equilibrium Corresponding nitrogen concentration The third relation, based on the third relation, the electron concentration of the silicon carbide wafer at equilibrium. The specific value is used to obtain the specific value of the nitrogen concentration of the silicon carbide wafer.

2. The method for measuring the nitrogen concentration of a silicon carbide wafer according to claim 1, characterized in that, A silicon carbide wafer after electrostatic removal treatment is provided, and a first contact potential of a surface of the silicon carbide wafer is measured The step specifically comprises: Provides silicon carbide wafers after electrostatic removal treatment and provides gold samples with known work functions; scanning the silicon carbide wafer and the gold standard sample under a microscope, and measuring a first contact potential difference between the silicon carbide wafer surface and a probe of the microscope a second contact potential difference between the gold standard sample surface and the probe of the microscope ; Based on the first contact potential difference The second contact potential difference The first contact potential on the surface of the silicon carbide wafer is calculated from the work function of the gold sample. .

3. The method for measuring the nitrogen concentration of a silicon carbide wafer according to claim 2, characterized in that, Based on the first contact potential difference The second contact potential difference The first contact potential on the surface of the silicon carbide wafer is calculated using the work function of the gold standard sample. The calculation process specifically includes: said first contact potential difference wherein denotes the potential of the probe surface, denotes the first contact potential of the silicon carbide wafer surface; said second contact potential difference wherein denotes the potential of the probe surface, denotes the second contact potential of the gold label surface; Among them, due to , , Given that the first contact potential on the surface of the silicon carbide wafer is obtained, .

4. The method for measuring the nitrogen concentration of a silicon carbide wafer according to claim 1, characterized in that, Establishing the first contact potential Corresponding to the conduction band bottom energy of the silicon carbide wafer and Fermi level energy The steps of the first relation specifically include: establishing the first contact potential. Corresponding electron affinity The conduction band bottom energy of the silicon carbide wafer and Fermi level energy The first relation; wherein the first relationship is: , wherein, represents a conduction band minimum energy of the silicon carbide wafer and a Fermi level energy of the silicon carbide wafer, represents an electron affinity.

5. The method of claim 1, wherein: Establish the conduction band bottom energy of the silicon carbide wafer. and Fermi level energy The difference corresponds to the electron concentration of the silicon carbide wafer at equilibrium. The steps of the second relation specifically include: Establish conduction band bottom energy and Fermi level energy The difference between the silicon carbide wafer and the room temperature at which the silicon carbide wafer is located. The Boltzmann constant corresponding to the silicon carbide wafer. The effective state density within the conduction band of the silicon carbide wafer. Corresponding to the electron concentration of the silicon carbide wafer at equilibrium The second relation wherein the second relationship is: an electron concentration of the silicon carbide wafer at equilibrium wherein, represents an effective state density in a conduction band of the silicon carbide wafer, represents a corresponding Boltzmann constant of the silicon carbide wafer, represents a room temperature at which the silicon carbide wafer is located.

6. The method for measuring the nitrogen concentration of a silicon carbide wafer according to claim 5, characterized in that, Effective state density in the conduction band of the silicon carbide wafer The formula is: In the formula, This indicates the equivalent number of valleys in the conduction band of the silicon carbide wafer. It is the effective mass of a trough state density in the conduction band of the silicon carbide wafer. This represents the electron mass in free space of the silicon carbide wafer. This indicates the room temperature at which the silicon carbide wafer is located.

7. The method of claim 1, wherein the step of measuring the nitrogen concentration of the silicon carbide wafer is performed by secondary ion mass spectroscopy. The third relation is: In the formula, This represents the effective state density within the conduction band of the silicon carbide wafer. This indicates the nitrogen concentration of the silicon carbide wafer. This represents the ionization energy of nitrogen. The degeneracy factor representing the donor, This represents the Boltzmann constant corresponding to the silicon carbide wafer. This indicates the room temperature at which the silicon carbide wafer is located.

8. The method of claim 1, wherein: The steps for providing a silicon carbide wafer after electrostatic removal treatment specifically include: providing a silicon carbide wafer to be tested; immersing the silicon carbide wafer in a hydrofluoric acid solution to remove the oxide layer on the surface of the silicon carbide wafer; then washing away the residual hydrofluoric acid on the surface of the silicon carbide wafer with distilled water; and then using an electrostatic gun or an ion fan to air-sweep the surface of the silicon carbide wafer to remove surface static electricity, thereby obtaining a silicon carbide wafer after electrostatic removal treatment.

9. The method of claim 2, wherein the step of measuring the nitrogen concentration of the silicon carbide wafer is performed by secondary ion mass spectroscopy. The first contact potential difference between the surface of the silicon carbide wafer and the probe of the microscope The second contact potential difference between the gold sample surface and the microscope probe The measurements were obtained by randomly selecting a scanning area from the surface of the silicon carbide wafer and the surface of the gold sample, respectively.

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