A method for calculating the material delocalization threshold energy based on ab initio molecular dynamics method

Abstract

The present invention provides a method for calculating the off-site threshold energy of a material based on an ab initio molecular dynamics method, which belongs to the field of simulation technology. The method comprises: establishing a system model corresponding to the material; setting simulation parameters, using an ab initio molecular dynamics method to simulate and calculate the off-site threshold energy of the system model, and obtaining the architecture after the evolution is completed, wherein the simulation parameters include a PKA preset energy; determining the new PKA energy required for subsequent simulation calculations according to the state of the architecture, and performing simulation calculations again until a stable defect is generated in the architecture for the first time, obtaining the PKA energy at this time, and determining it as the off-site threshold energy of the material. The present invention solves the problem that the off-site threshold energy of semiconductor materials cannot be quantitatively and accurately calculated, and the method has clear logic, simple steps and is easy to operate.

Description

Technical Field

[0001] The present invention relates to the field of simulation technology, and in particular to a method for calculating material delocalization threshold energy based on ab initio molecular dynamics method. Background Art

[0002] When semiconductor electronic devices are in a space environment for a long time, the semiconductor materials in the devices will be damaged by radiation from charged particles in space. Defects caused by radiation damage are mainly generated through ionization damage and displacement damage. In order to clearly understand the generation and formation mechanism of displacement defects, it is necessary to study the entire process of primary knockout particle (PKA) cascade collision, high temperature annealing, and finally stabilization in the defect evolution.

[0003] In the entire defect evolution process, the material's off-threshold energy is a crucial parameter. The off-threshold energy is the minimum energy that can make atoms move and form stable defects in the material. From its definition, it is not difficult to see that the value of the material's off-threshold energy plays a key role in the generation of PKA and the subsequent cascade process. Obtaining the accurate off-threshold energy value of the corresponding material is the basis of the entire simulation cascade process and an important guarantee for the correctness of the simulation results.

[0004] Currently, there are many methods to obtain the delocalization threshold energy value. Most of them use molecular dynamics method to simulate the delocalization threshold energy. However, molecular dynamics calculation is extremely dependent on empirical potential function. Due to the accuracy of empirical potential function, the delocalization threshold energy value calculated by molecular dynamics method often has deviations and low accuracy. Summary of the invention

[0005] The problem solved by the present invention is that the molecular dynamics method is often used in the prior art to simulate and calculate the delocalization threshold energy of materials. However, this method is limited by the accuracy of the empirical potential function, resulting in low calculation accuracy and the calculated delocalization threshold energy value often has a large deviation.

[0006] In order to solve the above problems, the present invention provides a method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method, comprising:

[0007] Step S1, establishing a system model corresponding to the material;

[0008] Step S2, setting simulation parameters, using ab initio molecular dynamics method to simulate and calculate the off-site threshold energy of the system model, and obtaining the system structure after the evolution is completed, wherein the simulation parameters include the PKA preset energy;

[0009] Step S3, determining the new PKA energy required for subsequent simulation calculations according to the state of the architecture, and performing simulation calculations again until a stable defect is first generated in the architecture, obtaining the PKA energy at this time, and determining it as the off-site threshold energy of the material.

[0010] Preferably, the step S3 specifically includes:

[0011] Determine whether there are stable defects in the initial structure evolved under the preset energy of PKA;

[0012] When the stable defect exists in the initial structure, the preset PKA energy is used as the initial energy, and a new PKA energy required to be applied in the subsequent simulation is determined according to the first method;

[0013] When the stable defect does not exist in the initial structure, the PKA preset energy is increased in a preset energy step size until a stable defect is generated in the system structure, the PKA energy at this time is obtained as the initial energy, and the new PKA energy required to be applied in the subsequent simulation is determined according to the first method.

[0014] Preferably, determining the new PKA energy required for subsequent simulation according to the first method comprises:

[0015] The new PKA energy required for subsequent simulations is determined in alternation with the first principle and the second principle, wherein the first principle is: when there are stable defects in the system structure, reduce the energy of PKA and perform the simulation again, and the second principle is: when there are no stable defects in the system structure, increase the energy of PKA and perform the simulation again.

[0016] Preferably, the determining of the new PKA energy required for subsequent simulation according to the first method specifically includes:

[0017] Decreasing the initial energy with a first set energy step length until no stable defects are generated in the system structure, and obtaining the PKA energy at this time as the first energy;

[0018] Increasing the first energy by a second set energy step length until a stable defect is generated in the system structure, and obtaining the PKA energy at this time as a second energy;

[0019] The second energy is determined as the off-site threshold energy of the material, or the second energy is simulated continuously in a decreasing and increasing manner according to different set energy steps until a stable defect is generated in the system structure, and the PKA energy at this time is obtained as the nth energy; the nth energy is determined as the off-site threshold energy of the material; wherein n is an integer greater than or equal to 3, and the first set energy step to the nth set energy step decrease successively.

[0020] Preferably, the method further comprises: repeating the step S1, the step S2 and the step S3 for different crystal orientations of the material to obtain off-location threshold energy values ​​for different crystal orientations.

[0021] Preferably, the simulation parameters also include ensemble, simulation time step and evolution time.

[0022] Preferably, the simulation time step is 0.5fs.

[0023] Preferably, the evolution time is 2000 simulation time steps.

[0024] Preferably, the ensemble is a NVE ensemble.

[0025] Preferably, the establishing of the system model corresponding to the material comprises: meshing the irradiated device to obtain a simulation box, and establishing a system model having a size equal to that of the simulation box.

[0026] The advantages of the present invention compared to the prior art are:

[0027] The present invention solves the problem that the off-site threshold energy of semiconductor materials cannot be quantitatively and accurately calculated. The present invention performs simulation based on the ab initio molecular dynamics method, obtains the architecture after the evolution is completed, determines the new PKA energy according to the state of the architecture, and performs simulation again, thereby obtaining the off-site threshold energy of the material through multiple adjustments of the PKA energy and multiple simulation processes, that is, the PKA energy when a stable defect is first generated in the architecture. The present invention uses ab initio molecular dynamics to solve the problem of low accuracy of the empirical potential function, and has clear logic, simple steps and easy operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of a method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the silicon material in an embodiment of the present invention;

[0030] Figure 3 Flow chart of a method for calculating material delocalization threshold energy in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] See also Figure 1 As shown, the embodiment of the present invention proposes a method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method, comprising:

[0033] Step S1, establishing a system model corresponding to the material;

[0034] Step S2, setting simulation parameters, using ab initio molecular dynamics method to simulate and calculate the off-site threshold energy of the system model, and obtaining the system structure after the evolution is completed, wherein the simulation parameters include the PKA preset energy;

[0035] Step S3, determining the new PKA energy required for subsequent simulation calculations according to the state of the architecture, and performing simulation calculations again until a stable defect is first generated in the architecture, obtaining the PKA energy at this time, and determining it as the off-site threshold energy of the material.

[0036] The method for calculating the material delocalization threshold energy described in the present invention can be applied to various types of semiconductor materials.

[0037] According to the present invention, firstly, a system model corresponding to semiconductor materials is established. Specifically, it includes: meshing the irradiated device, setting a simulation box of appropriate size according to the simulation situation, and obtaining the PKA information in each simulation box to establish a system model of the same size as the simulation box. The PKA information includes parameters such as PKA energy and type. Taking the Si system as an example, the Si unit cell can be expanded 5 times in the x, y and z directions to establish a Si structure of the same size as the box for subsequent simulation processes, such as Figure 2 The figure shows a schematic diagram of the structure of Si material used to calculate the off-site threshold energy.

[0038] According to the present invention, the simulation parameters are then set, and the ab initio molecular dynamics method (AIMD) is used to perform a simulation calculation of the delocalization threshold energy. The so-called delocalization threshold energy refers to the minimum energy that can cause atoms in the material to move and form stable defects in the material. Therefore, the simulation parameters include at least the PKA preset energy. In a specific implementation, the PKA energy in the simulation box obtained in step S1 can be used as the PKA preset energy input here, and the incident velocity of the PKA is given by the energy. In addition, the simulation parameters also include parameters such as the ensemble, simulation step, and evolution time. Preferably, the NVE (system particle number, volume, and energy remain unchanged) ensemble is selected for simulation, and the simulation time step is set to 0.5fs, and the simulation runs a total of about 2000 time steps.

[0039] In general calculations, the AIMD data file only contains the coordinate information of the atoms but not the velocity information of the atoms. For the calculation of the off-position threshold energy, the velocity information of the atoms needs to be included in the AIMD data file. The specific application method is to list the velocity components (vx, vy, vz) of each atom in three directions after describing the position information (xyz coordinates) of all atoms in the system. It should be noted that the velocity components of the atoms need to correspond one-to-one with the position information of the atoms. For example, the first line of velocity corresponds to the atomic velocity information in the first line of the atomic position information.

[0040] According to the present invention, after the simulation calculation is completed, the evolution of the final state of the structure is statistically analyzed, and the state of the system structure after the evolution is completed is observed. According to the definition of the off-site threshold energy, it can be seen that the information of the stable defects in the system structure is observed, that is, the PKA energy required for the subsequent simulation to continue is determined according to whether there are stable defects in the system structure. The determination principle is: when there are stable defects in the system structure, the PKA energy is reduced and the simulation is performed again. When there are no stable defects in the system structure, the PKA energy is increased and the simulation is performed again. The simulation and statistics are repeated until the minimum energy for generating stable defects is found, and the minimum energy is determined as the off-site threshold energy of the material.

[0041] In some implementation modes, step S3 specifically includes:

[0042] Determine whether there are stable defects in the initial structure evolved under the preset energy of PKA;

[0043] When the stable defect exists in the initial structure, the preset PKA energy is used as the initial energy, and a new PKA energy required to be applied in the subsequent simulation is determined according to the first method;

[0044] When the stable defect does not exist in the initial structure, the PKA preset energy is increased in a preset energy step size until a stable defect is generated in the system structure, the PKA energy at this time is obtained as the initial energy, and the new PKA energy required to be applied in the subsequent simulation is determined according to the first method.

[0045] Among them, the first method specifically includes: determining the new PKA energy required for subsequent simulations in an alternating manner according to the first principle and the second principle, the first principle being: when there are stable defects in the system structure, reducing the energy of PKA and performing re-simulation, the second principle being: when there are no stable defects in the system structure, increasing the energy of PKA and performing re-simulation.

[0046] Specifically, the initial energy is decreased with a first set energy step length until no stable defects are generated in the system structure, and the PKA energy at this time is obtained as the first energy;

[0047] Increasing the first energy by a second set energy step length until a stable defect is generated in the system structure, and obtaining the PKA energy at this time as a second energy;

[0048] The second energy is determined as the delocalization threshold energy of the material, or the second energy is simulated continuously in a decreasing and increasing manner according to different set energy steps until a stable defect is generated in the system structure, and the PKA energy at this time is obtained as the nth energy; the nth energy is determined as the delocalization threshold energy of the material; wherein n is an integer greater than or equal to 3, and the first set energy step to the nth set energy step decrease successively.

[0049] For example, based on the second energy obtained above, the second energy is decreased by a third set energy step until no stable defects are generated in the system structure, and the PKA energy at this time is obtained as the third energy;

[0050] ...(The ellipsis indicates that the order is in descending and ascending order)

[0051] Increasing the n-1th energy with the nth set energy step length until a stable defect is generated in the system structure, and obtaining the PKA energy at this time as the nth energy; wherein the first set energy step length, the second set energy step length, the third set energy step length, ..., the nth set energy step length decrease in sequence;

[0052] The second energy, the third energy, . . . , or the nth energy may be determined as the off-site threshold energy of the material.

[0053] It should be understood that, in theory, the PKA energy when stable defects begin to be generated in the system structure is the minimum energy. In this embodiment, after obtaining the PKA energy through the above-mentioned multiple decreasing and increasing cycles and simulating the calculation, the stable defects generated in the system structure are close to the stable defects generated for the first time. Therefore, the PKA energy after setting the number of simulations can be selected as the proposed minimum energy according to the demand situation, thereby obtaining the off-site threshold energy of the material.

[0054] The determination of the minimum energy for forming a stable defect is described below using a specific example.

[0055] First, a moderate value is given as the PKA energy for the first simulation calculation, that is, the PKA preset energy in the simulation parameters set in step S2, and the simulation calculation is performed with the preset energy;

[0056] When statistics are taken of the state of the architecture after the evolution is completed in step S3, if a stable defect is generated in the evolved structure under the PKA preset energy, the PKA preset energy is taken as the initial energy E0. Starting from E0, the PKA energy value is reduced by the first set energy step to obtain a new PKA energy, and the simulation is continued until no stable defects can be generated in the evolved structure. The PKA energy at this time is recorded as the first energy E1. At this time, starting from E1 again, the PKA energy value is increased by the second set energy step, and the simulation is continued until a stable defect can be generated. The PKA energy at this time is recorded as the second energy E2. In order to simplify the explanation, the material's off-site threshold energy Ed is set equal to E2.

[0057] Similarly, if no stable defects are generated in the evolving structure under the preset PKA energy, the PKA energy value is increased by the preset energy step and the simulation is continued until a stable defect is generated in the evolving structure, and the PKA energy at this time is recorded as E0; then starting from E0 again, the new PKA energy is determined and simulated in the above manner, and finally Ed is determined to be equal to E2.

[0058] For example, in combination Figure 3 As shown, the preset PKA energy is set to 5 eV; if no stable defects are generated in the system structure after the evolution is completed at 5 eV, the PKA energy is increased with a preset energy step of 5 eV starting from 5 eV, and then simulation is performed and a new PKA energy is assigned until a stable defect is generated in the system structure, and the PKA energy at this time is recorded as the initial energy E0; if a stable defect is generated in the system structure after the evolution is completed at 5 eV, 5 eV is used as the initial energy E0;

[0059] Then, starting from E0, the PKA energy is decreased by a first set energy step of 1 eV, and then simulation is performed and a new PKA energy is assigned until no stable defects are generated in the system structure, and the PKA energy at this time is recorded as the first energy E1; starting from E1, the PKA energy is increased by a second set energy step of 0.1 eV, and then simulation is performed and a new PKA energy is assigned until a stable defect is generated in the system structure, and the PKA energy at this time is recorded as the second energy E2, and the second energy E2 is determined as the off-site threshold energy Ed of the material.

[0060] In some of the embodiments, the method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method further includes: repeating the above step S1, the step S2 and the step S3 for different crystal orientations of the material to obtain the delocalization threshold energy values ​​of different crystal orientations. Taking silicon material as an example, the delocalization threshold energy of its typical crystal orientation is calculated, and the results are shown in Table 1. As an example to better illustrate the advantages of the method of the present invention, the delocalization threshold energy values ​​calculated under the classical force field are also recorded in Table 1. In Table 1, SW and Tersoff are two classical potential functions, Ed represents the delocalization threshold energy, and the "Direction" column represents different crystal orientations of silicon material.

[0061] Table 1:

[0062]

[0063]

[0064] It can be seen from Table 1 that the de-position threshold energy value calculated in this embodiment is smaller and closer to the actual value, which can illustrate that the method of the present invention can accurately describe the de-position threshold energy of the material.

[0065] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for calculating the material delocalization threshold energy based on ab initio molecular dynamics method, characterized in that: include: Step S1, establishing a system model corresponding to the material; Step S2, setting simulation parameters, using ab initio molecular dynamics method to simulate and calculate the off-site threshold energy of the system model, and obtaining the system structure after the evolution is completed, wherein the simulation parameters include the PKA preset energy; Step S3, determining a new PKA energy required for subsequent simulation calculations according to the state of the architecture, and performing simulation calculations again until a stable defect is first generated in the architecture, obtaining the PKA energy at this time, and determining it as the off-site threshold energy of the material; The step S3 specifically includes: determining whether there is a stable defect in the initial structure evolved under the preset PKA energy; when the stable defect exists in the initial structure, taking the preset PKA energy as the initial energy, and determining the new PKA energy required for subsequent simulation according to the first method; when the stable defect does not exist in the initial structure, increasing the preset PKA energy by a preset energy step length until a stable defect is generated in the system structure, obtaining the PKA energy at this time as the initial energy, and determining the new PKA energy required for subsequent simulation according to the first method; The method of determining the new PKA energy required for subsequent simulation according to the first method specifically includes: decreasing the initial energy by a first set energy step until no stable defects are generated in the system structure, and obtaining the PKA energy at this time as the first energy; increasing the first energy by a second set energy step until stable defects are generated in the system structure, and obtaining the PKA energy at this time as the second energy; determining the second energy as the off-site threshold energy of the material, or continuing to simulate the second energy in a decreasing and increasing manner according to different set energy steps until stable defects are generated in the system structure, and obtaining the PKA energy at this time as the nth energy; determining the nth energy as the off-site threshold energy of the material; wherein n is an integer greater than or equal to 3, and the first set energy step to the nth set energy step decrease in sequence.

2. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 1, characterized in that: Determining the new PKA energy required for subsequent simulation according to the first method includes: The new PKA energy required for subsequent simulations is determined in alternation with the first principle and the second principle, wherein the first principle is: when there are stable defects in the system structure, reduce the energy of PKA and perform the simulation again, and the second principle is: when there are no stable defects in the system structure, increase the energy of PKA and perform the simulation again.

3. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 1, characterized in that: The method further comprises: repeating the step S1, the step S2 and the step S3 for different crystal orientations of the material to obtain off-location threshold energy values ​​for different crystal orientations.

4. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 1, characterized in that: The simulation parameters also include the ensemble, simulation time step and evolution time.

5. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 4, characterized in that: The simulation time step is 0.5 fs.

6. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 5, characterized in that: The evolution time is 2000 simulation time steps.

7. The method for calculating the material delocalization threshold energy based on the ab initio molecular dynamics method according to claim 4, characterized in that: The ensemble is the NVE ensemble.

8. The method for calculating the material delocalization threshold energy based on ab initio molecular dynamics method according to claim 1, characterized in that: The establishing of the system model corresponding to the material comprises: meshing the irradiated device to obtain a simulation box, and establishing a system model having the same size as the simulation box.

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