Molecular dynamics simulation-based method for predicting defect rate and stress in 4H-SiC ion implantation process

Abstract

The invention provides a method for predicting crystal defect rate and stress in a 4H-SiC ion implantation process based on a molecular dynamics method, which comprises the following steps of: 1) establishing a 4H-SiC ion implantation theoretical model to obtain a data file of a structure; 2) constructing an input file containing simulation parameters and a potential function, namely an input file; 3) carrying out ion implantation simulation by adopting a molecular dynamics method, and outputting atomic coordinates and stress data; 4) drawing a change curve of the defect rate along with the injection dose according to the atomic trajectory; and 5) calculating the time average atomic stress of each atom under different injection doses according to the stress data, and exporting a stress distribution diagram. Molecular dynamics simulation is carried out on the process of ion implantation into the surface of 4H-SiC, the defect and atomic stress change of a crystal material in the process of ion implantation into 4H-SiC can be predicted, then the evolution mechanism of the defect and atomic stress in the 4H-SiC crystal under ion implantation is obtained, and theoretical guidance is provided for selection of ion implantation conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of crystal defect prediction, and in particular relates to a method for predicting defect rate and stress during ion implantation on a 4H-SiC surface. Background Art

[0002] Silicon carbide (SiC), as a typical representative of the third generation of semiconductor materials, has irreplaceable advantages in new energy vehicles, new energy power generation, rail transportation, aerospace, national defense and military industries due to its wide bandgap, high thermal conductivity and high electrical breakdown field strength. 4H crystalline SiC (4H-SiC) has the advantages of large bandgap, high critical breakdown electric field, high thermal conductivity and large electron saturation rate. Power devices based on 4H-SiC have higher conversion efficiency and switching frequency, and can easily achieve high-speed switching of high voltage and high current, so it has received widespread attention from the industry. However, the Si-C bond energy in SiC crystals is high, and impurity atoms are difficult to diffuse in it, so ion implantation technology has become the only choice for SiC doping. Ion implantation uses high-energy ions to bombard the lattice of hard and brittle materials, resulting in a series of atomic displacements and internal defects, thereby causing changes in the physical properties of the material. Molecular dynamics (MD) simulation methods have been successfully used to study the dynamics of defect evolution induced by ion implantation, which can help explain difficult problems that are difficult to solve with traditional analytical methods. MD simulation requires a short integration step, which can provide reference information for simulation processes with a time scale of less than nanoseconds. It has the advantage of transient observation of atomic motion evolution that macro measurement methods do not have, making up for the shortcomings of instrumental measurement of interatomic physical parameters. The duration from ion implantation into solid materials to the generation of displacement cascade reactions is generally in the range of femtoseconds to picoseconds. Therefore, MD simulation is a suitable method for studying low-energy cascades and recovery between atoms, especially for atomic collisions during ion implantation. At present, there is very limited work on using MD to study the process of Al ion implantation into 4H-SiC crystals. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting defect rate and stress during ion implantation of 4H-SiC. The method can directly obtain the defect rate and atomic stress changes on the 4H-SiC surface under different implantation ion types, implantation doses and implantation temperatures from molecular dynamics simulation, thereby providing guidance for the ion implantation process conditions of 4H-SiC.

[0004] The defect rate and stress prediction method in the process of ion implantation of 4H-SiC based on molecular dynamics simulation provided by the present invention adopts molecular dynamics simulation to simulate the microstructure in the process of ion implantation of 4H-SiC, calculates the defect rate and atomic stress changes, and then obtains the evolution mechanism of defects and atomic stress in 4H-SiC crystal under ion implantation, so as to provide theoretical guidance for the selection of ion implantation conditions; the method comprises the following steps:

[0005] Step 1: Establish the ion-implanted 4H-SiC surface model and obtain the data file of the structure;

[0006] Step 2: Construct an input file containing simulation parameters and potential functions, namely, the input file;

[0007] Step 3: Use molecular dynamics method to simulate ion implantation and output atomic coordinates and stress data;

[0008] Step 4: Draw a curve of defect rate versus implantation dose based on atomic trajectories;

[0009] Step 5: Calculate the time-averaged stress of each atom under different implantation doses from the stress data and derive the stress distribution diagram.

[0010] Further:

[0011] In step 1, the ion-implanted 4H-SiC surface model is established, specifically, based on the cif structure file of the 4H-SiC crystal, a flat plate model of the 4H-SiC (0001) surface is established using the Atomsk software, and exported to the data format file required by the molecular dynamics simulation software Lammps.

[0012] In step 2, the input file containing simulation parameters and potential functions is constructed, and the parameters for ion implantation simulation using Lammps software are specifically set, including: boundary condition ppf; force field parameter gw-zbl of 4H-SiC; force field parameter morse potential function of Si, C atoms and implanted ions; time interval, dose and kinetic energy of implanted ions; system temperature control method and ensemble NVT; the system temperature control method is to set the initial temperature to 298.15K, gradually increase it to the specified temperature according to the ion implantation conditions, and finally maintain the temperature.

[0013] In step 3, the molecular dynamics method is used to simulate ion implantation. Specifically, the atomic coordinates are derived to visualize the microstructural changes of the material. The Voronoi method (Chris H. Rycroft, Voro++: A three-dimensional Voronoi cell library in C++, Chaos 19, 041111 (2009)) is used to calculate the average volume of a single atom within a specified time interval, thereby calculating and deriving the time-averaged stress of the single atom. The stress tensor of a single atom is calculated by formula (1):

[0014]

[0015] In the formula, S aais the stress tensor in the x, y, and z directions, m is the atomic mass, and v aa is the velocity of the atom in the x, y, and z directions, W aa is the stress tensor contribution to the virial equation;

[0016] The stress of a single atom is the ratio of the stress tensor of the atom to its volume, calculated by equation (2):

[0017]

[0018] In the formula, σ atom is the stress of a single atom, V atom is the volume of a single atom; S atom is the atomic stress tensor, specifically:

[0019] S atom =S xx +S yy +S zz , #(3)

[0020] Among them, S xx , S yy , S zz They are represented as the stress tensors of atoms in the x-, y-, and z-directions respectively.

[0021] In step 4, the defect rate refers to the percentage of atoms in the 4H-SiC surface model that deviate from their original lattice positions during the ion implantation process. The atomic trajectories are processed using the Identify diamond structure method in the ovito software, and the number of Other, Cubic diamond and Hexagonal diamond crystal forms is counted. The percentage of Other in the total number is the defect rate.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] The invention provides a method for predicting the defect rate and stress of a material during ion implantation of 4H-SiC based on molecular dynamics simulation. The method adopts molecular dynamics to simulate the microstructure during ion implantation of 4H-SiC, calculates the defect rate and atomic stress changes, and further obtains the evolution mechanism of defects and atomic stress in a 4H-SiC crystal during ion implantation, thereby providing theoretical guidance for the selection of ion implantation conditions. The method is of great significance for characterizing the microstructure and performance changes of a 4H-SiC material during ion implantation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention provides a flow chart for predicting defect rate and stress during 4H-SiC ion implantation by molecular dynamics simulation.

[0025] Figure 2 Schematic diagram of 4H-SiC ion implantation model.

[0026] Figure 3 Schematic diagram of the defect rate change during Al ion implantation.

[0027] Figure 4 Schematic diagram of atomic stress distribution during Al ion implantation. DETAILED DESCRIPTION

[0028] The present invention is further described below by way of embodiments in conjunction with the accompanying drawings.

[0029] according to Figure 1 As shown, the defect rate and stress prediction method in the ion implantation process of 4H-SiC based on molecular dynamics simulation of the present invention comprises the following steps: step 1: establishing an ion implantation 4H-SiC surface model to obtain a data file of the structure; step 2: constructing an input file containing simulation parameters and potential functions, i.e., an input file; step 3: using a molecular dynamics method to perform ion implantation simulation, and outputting atomic coordinates and stress data; step 4: drawing a curve of defect rate changing with implantation dose according to atomic trajectories; step 5: calculating the time-averaged stress of each atom under different implantation doses from the stress data, and deriving a stress distribution diagram.

[0030] The following is the aluminum ion (Al + )-implanted 4H-SiC crystal is taken as the research object, and the steps of the method for predicting the defect rate and stress in the process of 4H-SiC ion implantation by molecular dynamics simulation in an embodiment of the present invention are described in more detail.

[0031] (1) Establish an ion-implanted 4H-SiC surface model. Based on the original cif file of 4H-SiC, use Atomsk software to expand the cell in three directions to establish a 19×33×16 supercell and add The vacuum is used to obtain the flat plate model of the 4H-SiC (0001) surface and exported as a data format file. The model contains a total of 180576 atoms and the box size is Its structure is as Figure 2 As shown, the bottom 4 layers of atoms are fixed and the thickness of the heat bath layer is set to The upper part of the heat bath layer is set as a Newton layer.

[0032] (2) Construct an input file containing simulation parameters and potential functions. Determine the necessary parameters for molecular dynamics simulation of ion implantation in Lammps software: Si-C interaction uses gw-zbl potential function, Si, C-Al +The interaction of the morse potential function is used; the initial temperature of the system is set to 298.15K, and the system temperature is adjusted according to the injection conditions; the time step is set to 0.001ps; the boundary conditions are ppf (period-period and fixed), the heat bath layer ensemble uses NVT (Constant Number, Volume, Temperature), and the Newton layer ensemble uses NVE (Constant Number, Volume, Energy); the injection of Al + The time interval is 10ps and the implantation dose is 0.9×10 14 / cm 2 , the initial kinetic energy is 3 keV, and the injection angle is 7°.

[0033] (3) The molecular dynamics method is used to calculate the ion implantation process. The complete ion implantation process consists of two stages. The first stage is ion implantation at 298.15K, which lasts for 2ns. The second stage is simulated annealing of the system. The annealing temperature is set to 2023.15K, the duration is 2.2ns, and the total simulation time is 4.2ns. Then the molecular dynamics simulation is started to output the atomic coordinates and stress data.

[0034] (4) The output atomic coordinate trajectory is processed using Ovito software, and the Identify diamond structure method is used to calculate the number of three crystal forms: Other, Cubic diamond and Hexagonal diamond. The defect rate curve over time is output, such as Figure 3 shown. Figure 3 Indicates the change of defect rate with simulation time in ion implantation simulation. The whole ion implantation process consists of two stages, namely the ion implantation stage and the simulated annealing stage after implantation. + The implantation causes lattice damage, which leads to defects. The higher the operating temperature, the higher the defect rate. During the simulated annealing process, the material damage is repaired.

[0035] (5) The Voronoi method is used to calculate the average volume of a single atom within a specified time interval, from which the time-averaged stress of a single atom is derived, and the atomic stress distribution of the model section is observed, such as Figure 4 shown. Figure 4 Presentation Al + Atomic stress distribution of 4H-SiC during implantation, with red representing positive stress and blue representing negative stress. As the implantation dose increases, the damaged area expands.

[0036] The method provided in the above embodiment can be used to simulate Al +Defects and atomic stress changes during implantation of 4H-SiC (0001) surface and visualization of the ion implantation process.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the specific implementation methods of the present invention, but those skilled in the art should understand that the present invention is not limited to the details of the above exemplary embodiments, does not deviate from the purpose and scope of the technical solution of the present invention, and modifications or equivalent replacements of the technical solution of the present invention are all covered by the protection scope of the present invention.

Claims

1. A method for predicting defect rate and stress in ion implantation of 4H-SiC based on molecular dynamics analysis, characterized in that: Molecular dynamics was used to simulate the microstructure of 4H-SiC during ion implantation, and the defect rate and atomic stress changes were statistically calculated. The evolution mechanism of defects and atomic stress in 4H-SiC crystals under ion implantation was then obtained. The specific steps are as follows: Step 1: Establish the ion-implanted 4H-SiC surface model and obtain the data file of the structure; Step 2: Construct an input file containing simulation parameters and potential functions, namely, the input file; Step 3: Use molecular dynamics method to simulate the ion implantation process and output atomic coordinates and stress data; Step 4: Draw a curve of defect rate versus implantation dose based on atomic trajectories; Step 5: Calculate the time-averaged atomic stress of each atom under different implantation doses from the stress data and derive the stress distribution diagram.

2. The prediction method according to claim 1, characterized in that: The ion-implanted 4H-SiC surface model is established as described in step 1. Specifically, based on the cif structure file of the 4H-SiC crystal, the slab model of the 4H-SiC (0001) surface is established using the Atomsk software and exported to the data format file required by the molecular dynamics simulation software Lammps.

3. The prediction method according to claim 2, characterized in that: The step 2 described constructing an input file containing simulation parameters and potential functions, and specifically setting the parameters for ion implantation simulation using Lammps software, including: boundary condition ppf, force field parameter gw-zbl of 4H-SiC, force field parameter morse potential function of Si, C atoms and implanted ions, time interval, dose and kinetic energy of implanted ions, temperature control method and ensemble NVT; the temperature control method is to set the initial temperature to 298.15K, gradually increase it to the specified temperature according to the ion implantation conditions, and finally maintain the temperature.

4. The prediction method according to claim 1, characterized in that: In step 3, the molecular dynamics method is used to simulate the ion implantation process. Specifically, the atomic coordinates are derived to visualize the microstructural changes of the material, and the Voronoi method is used to calculate the average volume of a single atom within a specified time interval, thereby calculating and deriving the time-averaged stress of the single atom; wherein the stress tensor of a single atom is calculated by formula (1): In the formula, S aa is the stress tensor in the x, y, and z directions, m is the atomic mass, and v aa is the velocity of the atom in the x, y, and z directions, W aa is the stress tensor contribution to the virial equation; The stress of a single atom is the ratio of the stress tensor of the atom to its volume, calculated by equation (2): In the formula, σ atom is the stress of a single atom, V atom is the volume of a single atom; S atom is the atomic stress tensor, specifically: S atom =S xx +S yy +S zz , #(3) Among them, S xx , S yy , S zz They are represented as the stress tensors of atoms in the x-, y-, and z-directions respectively.

5. The prediction method according to claim 1, characterized in that: In step 4, the defect rate refers to the percentage of atoms in the 4H-SiC surface model that deviate from their original lattice positions during the ion implantation process. The calculation method is: the atomic trajectories are processed using the Identify diamond structure method in the Ovito software, and the number of Other, Cubicdiamond and Hexagonal diamond crystal forms is counted, where the percentage of Other in the total number is the defect rate.

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