CN108517559B - A method for assisted control of ion implantation time based on Monte Carlo simulation - Google Patents

Abstract

The invention belongs to the application field of ion implantation, in particular to a method for assisted control of ion implantation time based on Monte Carlo simulation. Based on SRIM, the invention simulates argon ion implantation into strontium titanate crystal, takes each unit time as a segment, and combines repeated iterative calculations to control the time or dose of ion implantation and other factors to precisely control the oxygen vacancy concentration. Meaning control time. Solved the problem that time parameters cannot be set in SRIM simulation. By dividing the time into each unit time, and continuously advancing the solution in unit time, a relationship between time and the thickness of the amorphous layer is finally obtained, which can assist in the actual experiment process. Ion implantation dose control. It is a set of simulation calculation method with practical experimental significance, which avoids determining the injection time only by relying on the experimenter's experience in the experiment.

Description

A method for assisted control of ion implantation time based on Monte Carlo simulation

technical field

The invention belongs to the application field of ion implantation, in particular to a method for assisted control of ion implantation time based on Monte Carlo simulation.

Background technique

Monte Carlo method, also known as random sampling or statistical experimental method. Its basic idea is to obtain the frequency of occurrence of something or the average value of this random variable by means of experiments, so as to obtain the solution of this problem. Since traditional empirical methods cannot approximate the real physical process, it is difficult to obtain satisfactory results from them. The Monte Carlo method can realistically simulate the actual physical process, so the results obtained are very consistent with the actual situation. Commonly used Monte Carlo programs are MORSE, EGS, SRIM, etc. As a set of open source ion implantation simulation software, SRIM is currently the most widely used simulation ion implantation software. SRIM (The Stopping and Range of Ions in Matter) is a set of programs that calculate the stop and range of ions in matter.

In practical research, we usually modify a certain substance by ion implantation. For example, by doping some ions, oxygen vacancies can be generated on the oxide surface to obtain a conductive layer. In the experimental process, we often need to adjust the required oxygen vacancy concentration and the thickness of the amorphous layer by adjusting the dose of ion implantation. For example, strontium titanate is a typical perovskite crystal, which has richer physical properties due to its low atomic density and easy phase transition. Using doping, thin film and other methods, it is possible to change its chemical composition to control its physical properties. Strontium titanate is treated by argon ion bombardment. Since the diffusion rate of oxygen is much faster than that of strontium and titanium, more oxygen atoms are etched away during the bombardment process, and oxygen vacancies are formed on the surface of strontium titanate, so that titanate The strontium surface has a high-mobility, high-conductivity conductive layer. In the process of argon ion bombardment, we need to adjust the oxygen vacancy concentration by adjusting the implantation dose of argon ions. However, in the experimental process, the implantation dose of argon ions is determined by experimental experience. Although the oxygen vacancy concentration and the implantation dose are proportional in the experiment, considering the sputtering effect in the experimental process, the final sample The oxygen vacancy concentration cannot be precisely controlled, so the required oxygen vacancy concentration and the thickness of the amorphous layer cannot be accurately obtained only by experimental experience.

As we all know, SRIM can simulate the ion implantation process and obtain the oxygen vacancy concentration, but the simulation parameters of SRIM cannot set the time and dose. etching effect. Therefore, if we only rely on SRIM to simulate the initial state of the crystal, we can only obtain the approximate distribution trend of each atom, and cannot approximate the actual experimental process.

SUMMARY OF THE INVENTION

In view of the above problems or deficiencies, in order to solve the technical problems that the controllability of obtaining oxygen vacancies through ion implantation in experiments is not high and the relationship between time and concentration cannot be obtained by SRIM simulation, the present invention provides a Monte Carlo simulation based auxiliary control ion A method of injecting time.

The technical scheme adopted in the present invention is:

Step 1. Use SRIM to simulate the implantation of argon ions into the strontium titanate crystal, and calculate the oxygen vacancy concentration V ₁ and the thickness D ₁ of the amorphous layer. At the same time, the etched density ρ ₁ and thickness d ₁ are calculated according to the sputtering ratio. At this time, it is the equivalent injection amount of the first unit time.

Step 2. According to the simulation result of Step 1, set two layers of target materials, the first layer is the etched strontium titanate layer with density ρ ₁ and thickness d ₁ , and the second layer is strontium titanate crystal, and then use SRIM simulates the implantation of argon ions into the bilayer target material, and calculates the oxygen vacancy concentration V ₂ and the thickness of the amorphized layer D ₂ . At the same time, the etched density ρ ₂ and thickness d ₂ are calculated according to the sputtering ratio. At this time, it is the equivalent injection amount of the second unit time.

Step 3. According to the methods of Step 1 and Step ₂ , continuously accumulate and calculate the oxygen _{vacancy concentrations} V ₃ , V ₄ , _.

Step 4: Determine whether the calculated D _n meets the value required by the experimental requirements. If not, return to step 2 to continue the calculation. Until D _n meets the value required by the experiment, the calculation is stopped, and the relationship between the time and the thickness of the amorphous layer and the total distribution of each atom can be obtained.

Based on SRIM, the invention simulates argon ion implantation into strontium titanate crystal, takes each unit time as a segment, and combines repeated iterative calculations to control the time or dose of ion implantation and other factors to precisely control the oxygen vacancy concentration. Meaning control time.

Compared with the prior art, the benefits of the present invention are:

1. The invention solves the problem that time parameters cannot be set for SRIM simulation. It cleverly uses dividing time into each unit time, and continuously advances the solution in unit time, and finally obtains a relationship between time and the thickness of the amorphous layer.

2. The method obtains the relationship between the time and the thickness of the amorphous layer, which can assist the control of the ion implantation dose in the actual experiment process.

Description of drawings

Figure 1. Oxygen vacancy concentration distribution diagram (the hollow curve is the first unit time, and the solid curve is the second unit time);

Figure 2. Overall flow chart;

Fig. 3. Relationship between time and thickness of amorphized layer.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Set the experimental conditions: the implantation energy of argon ions is 300eV, the implantation dose per second is 10 ¹⁵ ion/cm ² , and the unit time is 1 second. When the oxygen vacancy concentration reaches 10% of the initial strontium titanate atomic concentration, it is regarded as The crystal is amorphized.

First, SRIM is used to simulate argon ion implantation into strontium titanate to obtain the number of atomic vacancies, and then the oxygen vacancy concentration V ₁ and the amorphous layer thickness D ₁ =12.266 angstroms are calculated for the first unit time. The oxygen vacancy distribution is shown as the hollow curve in Fig. 1.

According to the sputtering ratio of the simulation results in the previous step, the density ρ ₁ =4.886g/cm ³ and the thickness d ₁ =14.696 angstroms of strontium titanate after etching were calculated, and then SRIM was used to simulate the argon ion implantation of strontium titanate (at An etched layer with a density of ρ ₁ and a thickness of d ₁ is set before the strontium titanate crystal), and the oxygen vacancy concentration V ₂ and the amorphous layer thickness D ₂ =14.625 angstroms are also calculated for the second unit time. The oxygen vacancy distribution is shown as the solid curve in Figure 1.

Repeat the above steps in the same way, and the overall flow chart is shown in Figure 2. The calculation is stopped until the thickness D _n of the amorphous layer is calculated to meet the experimentally required thickness. The relationship between the acquisition time and the thickness of the amorphized layer is shown in FIG. 3 .

Based on SRIM, the present invention obtains oxygen vacancy concentration by simulating argon ion implantation into strontium titanate (density 5.113g/cm ³ , energy threshold oxygen 50eV, strontium 70eV, titanium 140eV) (the concentration at this time does not include etching effect) ), then, assuming that we need oxygen vacancies to occupy a certain value of the initial atomic concentration of strontium titanate, the crystal is considered to be amorphized, and the thickness of the amorphous layer is calculated, and the relationship between the time and the thickness of the amorphous layer is obtained through this algorithm, Until the thickness of the amorphous layer reaches the desired value, the dose that needs to be implanted in actual operation is finally obtained.

To sum up, it can be seen that the present invention can control the time and dose of ions to be implanted in the experiment by means of simulation, so as to avoid the time to be implanted by relying only on the experience of the experimenter in the experiment, which is a set of practical experimental significance. Simulation calculation method.

Claims (1)

1. A method for assisted control of ion implantation time based on Monte Carlo simulation, the concrete steps are as follows: Step 1. Use SRIM to simulate the implantation of argon ions into the strontium titanate crystal, and calculate the oxygen vacancy concentration V ₁ and the thickness D ₁ of the amorphous layer; at the same time, calculate the density ρ ₁ and thickness d ₁ after etching according to the sputtering ratio, At this time, it is the equivalent injection amount of the first unit time; Step 2. According to the simulation result of Step 1, set two layers of target materials, the first layer is the etched strontium titanate layer with density ρ ₁ and thickness d ₁ , and the second layer is strontium titanate crystal, and then use SRIM simulates the implantation of argon ions into the double-layer target material, and calculates the oxygen vacancy concentration V ₂ and the thickness of the amorphous layer D ₂ ; at the same time, according to the sputtering ratio, the etched density ρ ₂ and thickness d ₂ are calculated, which is the second Equivalent injection volume per unit time; Step 3. According to the methods of Step 1 and Step 2, continuously accumulate and calculate the oxygen vacancy concentrations V ₃ , V ₄ , ..., V _n and the thickness of the amorphous layer D ₃ , D ₄ , ..., D _n ; Step 4. Determine whether the calculated D _n meets the value required by the experimental requirements; if not, return to step 2 to continue the calculation until D _n meets the required value of the experiment, then stop the calculation, and the time and amorphous values can be obtained. The relationship between the thickness of the strontium titanate layer and the total atomic distribution; the judgment of D _n means that when the oxygen vacancy concentration reaches 10% of the initial strontium titanate atomic concentration, the crystal is considered to be amorphized, and the amorphous layer is calculated. Thickness, the relationship between the time and the thickness of the amorphous layer is obtained through this algorithm, until the thickness of the amorphous layer reaches the desired value.

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