CN108517559B

CN108517559B - Method for auxiliary control of ion implantation time based on Monte Carlo simulation

Info

Publication number: CN108517559B
Application number: CN201810184340.2A
Authority: CN
Inventors: 张万里; 王放; 曾慧中
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2018-03-07
Filing date: 2018-03-07
Publication date: 2020-12-29
Anticipated expiration: 2038-03-07
Also published as: CN108517559A

Abstract

The invention belongs to the field of application of ion implantation, and particularly relates to a method for assisting in controlling ion implantation time based on Monte Carlo simulation. The method is based on SRIM, simulates argon ion implantation strontium titanate crystal, takes each unit time as a subsection, and combines the factors of repeated iterative calculation to control the time or dosage of ion implantation and the like to accurately control the oxygen vacancy concentration, thereby obtaining the control time with experimental significance. The problem that the SRIM simulation cannot set time parameters is solved, the time is divided into each unit time, the unit time is used for continuously advancing and solving, finally, the relation between the time and the thickness of an amorphous layer is obtained, and the control of ion implantation dosage in the actual experiment process can be assisted. The injection time is prevented from being determined only by the experience of an experimenter in the experiment, and the method is a simulation calculation method with practical experiment significance.

Description

Method for auxiliary control of ion implantation time based on Monte Carlo simulation

Technical Field

The invention belongs to the field of application of ion implantation, and particularly relates to a method for assisting in controlling ion implantation time based on Monte Carlo simulation.

Background

The Monte Carlo (Monte Carlo) method, also known as random sampling or statistical experimental methods. The basic idea is to find the solution of the problem by experimentally obtaining the frequency of occurrence of a certain event or the average value of the random variable. Because the traditional empirical method cannot approach the real physical process, a satisfactory result is difficult to obtain from. The Monte Carlo method can truly simulate the actual physical process, so the obtained result is in good accordance with the reality. Common Monte Carlo programs are MORSE, EGS, SRIM, and the like. SRIM is currently the most widely used software for simulating ion implantation as a set of open source ion implantation simulation software. SRIM (the Stopping and Range of Ions in matter) is a set of programs that calculate the Stopping and Range of Ions in a substance, a Monte Carlo calculation that calculates the energy transferred to the target atom with each collision in detail, following the entry of an ion into the target.

In practical studies, we usually modify a substance by ion implantation, for example, doping some ions can generate oxygen vacancy on the surface of oxide to obtain a conductive layer. In the experimental process, the required oxygen vacancy concentration, the thickness of the amorphous layer and the like are often required to be regulated and controlled by regulating the ion implantation dosage. For example, strontium titanate is a typical perovskite crystal, and has more abundant physical properties due to the characteristics of low atomic density, easy phase transition and the like. The chemical components can be changed by doping, thinning and other methods, so that the physical properties of the material can be regulated and controlled. The strontium titanate is treated by argon ion bombardment, and because the diffusion speed of oxygen is much faster than that of strontium and titanium, more oxygen atoms are etched in the bombardment process, and oxygen vacancies are formed on the surface of the strontium titanate, so that the surface of the strontium titanate has a conductive layer with high mobility and high conductivity. During the argon ion bombardment process, the oxygen vacancy concentration needs to be regulated and controlled by adjusting the implantation dosage of the argon ions. However, in the experimental process, the implantation dose of the argon ions is determined by means of experimental experience, and although the oxygen vacancy concentration and the implantation dose in the experiment are in a proportional relation, the oxygen vacancy concentration of the final sample cannot be accurately controlled in consideration of the sputtering effect in the experimental process, so that the accurate required oxygen vacancy concentration and the thickness of the amorphous layer cannot be accurately obtained by means of the experimental experience only.

As is known, SRIM can simulate an ion implantation process and obtain an oxygen vacancy concentration, but simulation parameters of SRIM cannot set time and dose, that is, simulation of SRIM is only a certain time point, and cannot truly describe an etching effect in the ion implantation process. Therefore, if only the simulation of the initial state of the crystal by the SRIM is relied on, only the approximate distribution trend of each atom can be obtained, and the actual experimental process cannot be approached.

Disclosure of Invention

Aiming at the problems or the defects, the invention provides a method for assisting in controlling ion implantation time based on Monte Carlo simulation, in order to solve the technical problems that the controllability of obtaining oxygen vacancies through ion implantation is not high and SRIM simulation cannot obtain the relation between time and concentration in an experiment.

The technical scheme adopted by the invention is as follows:

step 1, simulating argon ion implantation into strontium titanate crystal by utilizing SRIM (surface plasmon resonance imaging), and calculating oxygen vacancy concentration V₁And amorphization layer thickness D₁. Meanwhile, the density rho of etching is calculated according to the sputtering proportion₁Thickness d₁. This time is the equivalent injection amount of the first unit time.

Step 2, setting two layers of target materials according to the simulated result in the step 1, wherein the first layer is density rho₁Thickness d₁The second layer is strontium titanate crystal, then uses SRIM to simulate argon ion injection into double-layer target material, calculates oxygen vacancy concentration V₂And amorphization layer thickness D₂. Meanwhile, the density rho of etching is calculated according to the sputtering proportion₂Thickness d₂. This is the equivalent injection amount per unit time of the second.

Step 3, continuously accumulating and calculating the oxygen vacancy concentration V according to the methods of the step 1 and the step 2₃、V₄、…、V_nAnd amorphization layer thickness D₃、D₄、…、D_n。

Step 4, judging the calculated D_nWhether the required values for the experimental requirements are met. If not, returning to the step 2 to continue the calculation. Up to D_nIf the numerical values required by the experiment are met, the calculation is stopped, and the relation between the time and the thickness of the amorphous layer and the total distribution condition of each atom can be obtained.

The method is based on SRIM, simulates argon ion implantation strontium titanate crystal, takes each unit time as a subsection, and combines the factors of repeated iterative calculation to control the time or dosage of ion implantation and the like to accurately control the oxygen vacancy concentration, thereby obtaining the control time with experimental significance.

Compared with the prior art, the invention has the advantages that:

1. the method solves the problem that the SRIM simulation can not set time parameters, skillfully divides the time into each unit time, and continuously advances to solve the time by the unit time, thereby finally obtaining the relation between the time and the thickness of the amorphous layer.

2. The method obtains the relation between time and the thickness of the amorphous layer, and can assist in controlling the ion implantation dosage in the actual experiment process.

Drawings

FIG. 1, oxygen vacancy concentration profile (open curve first unit time, filled curve second unit time);

FIG. 2, general flow diagram;

fig. 3, time versus amorphized layer thickness.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. Setting the experimental conditions: the implantation energy of argon ions was 300eV, and the implantation dose per second was 10¹⁵ion/cm²When the concentration of oxygen vacancies reached 10% of the initial concentration of strontium titanate atoms per 1 second, the crystal was considered to be amorphized.

Firstly, simulating argon ion implantation of strontium titanate by utilizing SRIM (surface plasmon resonance imaging) to obtain the number of each atomic vacancy, and then calculating the oxygen vacancy concentration V of the first unit time₁And amorphization layer thickness D₁12.266 angstroms. The oxygen vacancy profile is shown by the open curve in figure 1.

Calculating the density rho of the etched strontium titanate according to the sputtering proportion of the simulation result of the previous step₁＝4.886g/cm³And a thickness d₁14.696 angstroms and then implanting strontium titanate with SRIM simulated argon ions (a layer of density p is placed before the strontium titanate crystal)₁A thickness d₁Of the layer to be etched), the oxygen vacancy concentration V per unit time of the second unit time is also calculated₂And amorphization layer thickness D₂14.625 angstroms. The oxygen vacancy profile is shown by the solid curve in figure 1.

The above steps are repeated in the same way and the general flow chart is shown in fig. 2. Until the amorphized layer thickness D is calculated_nThe calculation is stopped when the thickness required in the experiment is satisfied. The obtained time versus the thickness of the amorphous layer is shown in fig. 3.

The invention is based on SRIM, and the strontium titanate (density 5.113 g/cm) is implanted by simulating argon ion³Energy threshold oxygen50eV, strontium 70eV, titanium 140eV) to obtain the oxygen vacancy concentration (the concentration at this time does not include etching effect), then, assuming that we need the oxygen vacancy to account for a certain value of the strontium titanate initial atom concentration, the crystal is regarded as being amorphized, the thickness of the amorphous layer is calculated, the relation between the time and the thickness of the amorphous layer is obtained through the algorithm until the thickness of the amorphous layer reaches the required value, and finally, the injection dosage required in the actual operation is obtained.

In summary, it can be seen that the present invention can control the time and dosage of ion implantation required in an experiment through a simulation method, so that the determination of the implantation time only depending on the experience of an experimenter in the experiment can be avoided, and the method is a set of simulation calculation methods with practical experimental significance.

Claims

1. A method for assisting in controlling ion implantation time based on Monte Carlo simulation comprises the following specific steps:

step 1, simulating argon ion implantation into strontium titanate crystal by utilizing SRIM (surface plasmon resonance imaging), and calculating oxygen vacancy concentration V₁And amorphization layer thickness D₁(ii) a Meanwhile, the density rho after etching is calculated according to the sputtering proportion₁Thickness d₁The equivalent injection amount of the first unit time is obtained;

step 2, setting two layers of target materials according to the simulated result in the step 1, wherein the first layer is density rho₁Thickness d₁The second layer is strontium titanate crystal, then uses SRIM to simulate argon ion injection into double-layer target material, calculates oxygen vacancy concentration V₂And amorphization layer thickness D₂(ii) a Meanwhile, the density rho of etching is calculated according to the sputtering proportion₂Thickness d₂The equivalent injection amount in the second unit time;

step 3, continuously accumulating and calculating the oxygen vacancy concentration V according to the methods of the step 1 and the step 2₃、V₄、…、V_nAnd amorphization layer thickness D₃、D₄、…、D_n；

Step 4, judging the calculated D_nWhether the required value of the experimental requirements is met; if not, return toStep 2, continuing to calculate until D_nIf the numerical values required by the experiment are met, the calculation is stopped, and the relation between the time and the thickness of the amorphous layer and the total distribution condition of each atom can be obtained; said D_nThe judgment of (1) means that the crystal is regarded as being amorphized when the oxygen vacancy concentration reaches 10% of the initial strontium titanate atom concentration, the thickness of the amorphized layer is calculated, and the relation between the time and the thickness of the amorphous layer is obtained through the algorithm until the thickness of the amorphous layer reaches the required value.