CN108154004B - Transition layer material selection method based on evaluation of bonding force of transition layer on epitaxial film and substrate - Google Patents

Abstract

The invention provides a transition layer material selection method based on evaluation of the bonding force between an epitaxial film and a substrate of the transition layer, belongs to the technical field of film growth theory, and in particular relates to a transition layer selection method. The present invention first establishes an interface model for several selected transition layer materials; then calculates the interface performance when no transition layer exists, and determines whether a transition layer is required; The interfacial properties of the transition layer and the transition layer/film, and comprehensively evaluate and rank the binding force of the transition layer to the substrate and the transition layer to the film according to the change in the net charge at the interface and the number of interatomic chemical bonds; As a result, the first 2 to 3 transition layer materials were selected. The invention solves the problems of long time and waste of manpower and material resources when determining whether a transition layer is required and which material is selected as the transition layer in the prior art. The present invention can be applied to the preparation of thin films.

Description

Selection of transition layer materials based on the evaluation of the bonding force between the transition layer epitaxial film and the substrate method

technical field

The invention belongs to the technical field of thin film growth theory, and particularly relates to a transition layer selection method.

Background technique

An interface is formed between the thin film and the substrate during the preparation of the thin film, and the properties of the interface, especially the bonding force between the thin film and the substrate, have an important influence on the preparation of the thin film and the performance of the thin film. If the film cannot be well combined on the substrate, not only more severe conditions are required in the preparation process, but also the prepared film is more likely to fall off, thus affecting the effective performance of the film. For epitaxial thin films, if there is a lack of good bonding with the substrate, the orientation deviation will also be caused, and it is even difficult to form epitaxy, and the prepared thin films are in polycrystalline form.

The growth of functional oxide films on Si substrates with oxide layers is a very common example. Functional oxide single crystals, especially metal oxides such as MgO, SrTiO, and yttrium _- stabilized zirconia (YSZ), have attracted the attention of researchers due to their potential applications in fields such as microelectronic device fabrication. But single crystal materials are expensive, and considering the integration of electronic devices with Si materials, functional oxide materials need to be epitaxially grown on Si. However, it is difficult to directly grow most oxides on Si substrates, and some oxides have problems with the penetration of Si substrate components at higher temperatures. At the same time, due to problems such as lattice mismatch, crystal structure difference, and incompatible thermal expansion coefficient, the interface between some oxide films and the Si substrate is very fragile, the bonding force is low, and there is a large residual stress. It is difficult to obtain high-quality metal oxide films directly on the substrate.

In order to solve these problems, a transition layer 2 (as shown in FIG. 1 ) can usually be deposited between the substrate and the thin film to enhance the bonding force between the thin film 3 and the substrate 1 and improve the growth quality of the thin film. For example, when a functional oxide film is prepared on a Si substrate, a TiN film is often used as a transition layer to improve the interface bonding force between the oxide film and the Si substrate. However, there are many kinds of substrate materials and thin film materials. For a specific substrate material and specific thin film material, it is difficult to determine whether a transition layer is required and what kind of material is required as a transition layer. The existing methods mainly focus on the possible transition layers. Experimenting with materials one by one will waste a lot of manpower and material resources and take a long time.

SUMMARY OF THE INVENTION

In order to solve the problems of long time and waste of manpower and material resources when determining whether a transition layer is required in the prior art and which material is selected as the transition layer, the invention further provides a transition layer based on the evaluation of the bonding force between the epitaxial film and the substrate of the transition layer. Material selection method.

The transition layer material selection method based on the evaluation of the bonding force between the transition layer epitaxial film and the substrate according to the present invention is realized by the following technical solutions:

Step 1: Select several transition layer materials according to the properties of the substrate material and the film material;

Step 2: Establish the required interface model; the specific process includes:

21) According to the lattice constant and lattice type of the crystal, respectively establish the crystal model of the substrate material, the transition layer material and the thin film material;

22) Based on the crystal model, the surface models of the substrate material, the transition layer material and the thin film material are established respectively according to the crystal plane index, the thickness and direction parameters of the surface are adjusted, and the supercell is established according to the lattice constant, so that the surfaces that will be combined into the interface are formed. The lattice constants of the surfaces of the two materials differ by less than 5%;

的真空层，形成晶体；23) Combine the constructed surface models into substrate/film, substrate/transition layer, transition layer/film interface models, and add a thickness not less than

the vacuum layer to form crystals;

Step 3: Calculate the interface properties when there is no transition layer, that is, the interface properties of the substrate/film. According to the change in the net charge at the interface and the number of interatomic chemical bonds, determine whether a transition layer is required; if a transition layer is required, carry out Step four;

The specific calculation steps of the interface properties of the substrate/film include:

31) Geometric optimization and property calculation of the substrate/thin film interface: Use the CASTEP module in the Material Studio material calculation software to perform geometric optimization and property calculation of the substrate/thin film interface, select the exchange correlation function and pseudopotential, and select the "geometric optimization". "task, get the structure of the substrate/film interface; set the accuracy, cut-off energy, and k-point value according to the size of the model, select the change in net charge and the number of chemical bonds between atoms in the Properties tab, and run the calculation;

32) Analysis of atomic charge and electron transfer at the interface: select the population analysis in the analysis of the CASTEP module, select the calculated .castep file as the result file, choose to assign the charge to the structure, and mark the charge after the geometry optimization. On each atom of the model of , compare the charge of atoms at the interface with the charge of atoms far away from the interface to obtain the net charge change at the substrate/film interface;

33) Analysis of the chemical bond population at the interface: in the population analysis, choose to assign chemical bonds to the structure, and obtain the interatomic chemical bond population at the substrate/film interface. The positive and negative signs of the population indicate the type of interaction, and a positive value Represents a covalent bond, a negative value represents an ionic bond, and the absolute value indicates the relative strength of the interaction force;

Step 4: Calculate the interface properties of the substrate/transition layer and the transition layer/thin film when the material within the range selected in Step 1 is used as the transition layer, and according to the change in the net charge at the interface and the number of interatomic chemical bonds, for When different materials are used as the transition layer, the transition layer comprehensively evaluates the bonding force of the substrate and the transition layer to the film, and selects the material that is effective for improving the bonding force of the substrate/film interface;

Step 5: Evaluate and sort the bonding force between the film and the substrate when the material selected in Step 4 is used as the transition layer; select the first 2 to 3 transition layer materials according to the sorting result.

The most prominent features and significant beneficial effects of the present invention are: the present invention utilizes material calculation software such as Material Studio to establish corresponding substrate/transition layer and transition layer/thin film material interface models, and adopts the first principles based on density functional theory. The simulation calculation is carried out to evaluate the bonding force between the film and the substrate from the point of view of the atomic and molecular level, the interaction between electrons and the formation of chemical bonds, and the appropriate transition layer material is selected according to the calculation and simulation results.

The influence of the transition layer on the bonding force of the substrate/film interface was evaluated by interface simulation calculation, and an appropriate evaluation standard was proposed.

Moreover, according to the effect of the transition layer on the bonding force of the substrate/film interface, the selection range of the transition layer is narrowed, and the selection of the transition layer material is guided, which greatly saves time and labor and material costs, such as Example 1, Example 2 and Example 3, the average time saving is 72%.

Description of drawings

Fig. 1 is the sample structure schematic diagram with transition layer;

Figure 2 shows the simulation results of the interface structure after the geometry optimization of the SiO ₂ (100)/TiN(100) interface;

Figure 3 shows the simulation results of the interface structure after the geometry optimization of the TiN(100)/MgO(100) interface;

Figure 4 is a graph showing the peak splitting results of the Ti1/2p peak of the X-ray photoelectron spectrum at the interface of SiO ₂ (100)/TiN(100)/MgO(100) etched to the SiO ₂ (100)/TiN(100) interface;

Fig. 5 is a graph showing the peak splitting results of the X-ray photoelectron spectrum Mg1s peak at the interface of TiN(100)/MgO(100) by etching the SiO ₂ (100)/TiN(100)/MgO(100) sample;

Figure 6 is a scanning electron microscope (SEM) photograph of the surface of the SiO ₂ (100)/MgO (100) sample after nano-scratch;

Among them: 1. Substrate, 2. Transition layer, 3. Thin film.

Detailed ways

Embodiment 1: The transition layer material selection method based on the evaluation of the bonding force between the epitaxial film and the substrate of the transition layer provided in this embodiment specifically includes the following steps:

Step 1. According to the properties of the substrate material and the film material, determine the selection range of the transition layer material that may be suitable for the substrate and the film material; in the selection process, the conventional transition layer, literature and experimental experience in the field can also be selected. Several possible transition layer materials, usually 5 to 8 are selected;

Step 2: Establish the required interface model; the specific process includes:

21) According to the lattice constant and lattice type of the crystal, respectively establish the crystal model of the substrate material, the transition layer material and the thin film material;

22) Based on the crystal model, the surface models of the substrate material, the transition layer material and the thin film material are established respectively according to the crystal plane index, the thickness and direction parameters of the surface are adjusted, and the supercell is established according to the lattice constant, so that the surfaces that will be combined into the interface are formed. The surfaces of the two materials have as similar lattice constants as possible, here defining the lattice constants of the surfaces of the surfaces of the two materials to be combined into an interface that differ by less than 5%;

的真空层，形成晶体；23) Combine the constructed surface models into substrate/film, substrate/transition layer, transition layer/film interface models, and add a thickness not less than

the vacuum layer to form crystals;

Step 3: Calculate the interface properties when there is no transition layer, that is, the interface properties of the substrate/film. According to the change in the net charge at the interface and the population of chemical bonds between atoms, determine whether a transition layer is required; if the transition layer is not required, End the transition layer material selection, if a transition layer is required, go to step 4;

The specific calculation steps of the interface properties of the substrate/film include:

31) Geometric optimization and property calculation of substrate/thin film interface: Use Material Studio material calculation software (Materials Studio is a simulation software specially developed for researchers in the field of materials science that can run on PC, regardless of configuration optimization, properties Prediction and X-ray diffraction analysis, as well as complex kinetic simulations and quantum mechanical calculations, can be obtained through some simple and easy-to-learn operations to obtain reliable data) The CASTEP module in the substrate/film interface for geometric optimization and property calculations , select the appropriate exchange correlation function and pseudopotential, and select the "geometric optimization" task to obtain the structure of the substrate/film interface; set the accuracy, cut-off energy, and k-point value (equivalent to a sampling density) according to the size of the model. In the tab, select the change in net charge and the population of chemical bonds between atoms, and run the calculation;

32) Analysis of atomic charge and electron transfer at the interface: select the population analysis in the analysis of the CASTEP module, select the calculated .castep file as the result file, choose to assign the charge to the structure, and mark the charge after the geometry optimization. On each atom of the model of , compare the charge of atoms at the interface with the charge of atoms far away from the interface to obtain the net charge change at the substrate/film interface;

33) Analysis of the chemical bond population at the interface: in the population analysis, choose to assign chemical bonds to the structure, analyze whether there are new chemical bonds related to the interface elements at the interface other than the chemical bonds inside the structure, and finally get the substrate. The population number of chemical bonds between atoms at the /film interface, the positive and negative signs of the population number indicate the type of interaction, the positive value represents covalent bonds, the negative value represents ionic bonds, and the absolute value indicates the relative strength of the interaction force;

The following analysis of the atomic fractional wave density of states at the interface can explain the change in charge amount and the formation of chemical bonds: Analysis of the atomic fractional wave density of states at the interface: select the atoms at the interface respectively, and select the density of states, fractional density of states in the analysis of the CASTEP module Wave density of states, import the results into the function drawing software (Matlab, Mathmatica, Maple, Origin, etc.) and re-draw into the partial wave density of states of each atom at the interface, compare with the partial wave density of states of atoms far away from the interface, and get Changes in net charge and the population of chemical bonds between atoms.

Step 4: Calculate the interface properties of the substrate/transition layer and the transition layer/thin film when the material within the range selected in Step 1 is used as the transition layer, and according to the change in the net charge at the interface and the number of interatomic chemical bonds, for When different materials are used as the transition layer, the transition layer comprehensively evaluates the bonding force of the substrate and the transition layer to the film, and selects the material that is effective for improving the bonding force of the substrate/film interface;

Step 5: Evaluate and sort the bonding force between the film and the substrate when the effective material selected in the step 4 is used as the transition layer; select the first 2 to 3 transition layer materials according to the sorting result.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the method for determining whether a transition layer is required in step 3 is:

According to the calculation results of the interface properties without the transition layer in step 3, it is determined whether a transition layer is required; The absolute value of the inter-chemical bond population is less than 0.10 (indicating that there is almost no interaction between atoms at the interface), and a transition layer needs to be introduced to improve the interface bonding force between the film and the substrate. Otherwise, if the net charge change between atoms at the interface is greater than If it is equal to 10% or the absolute value of the interatomic chemical bond population at the interface is greater than or equal to 0.10, it is not necessary to refer to the transition layer.

Other steps and parameters are the same as in the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that in step 4, the specific steps of comprehensively evaluating any material within the range selected in step 1 include:

For any material i within the range selected in step 1 as the transition layer:

41) Calculate the interface properties of the substrate/transition layer interface, and obtain the net charge amount change x _i at the substrate/transition layer interface and the absolute value y _i of the population of chemical bonds between atoms at the substrate/transition layer interface;

Calculate the interface properties of the transition layer/film interface, and obtain the net charge change x' _i of the transition layer/film interface and the absolute value of the interatomic chemical bond population y' _i at the transition layer/film interface;

42) Functional evaluation of transition layer: if x _i ≥ 10% or y _i ≥ 0.10, and at the same time x' _i ≥ 10% or y' _i ≥ 0.10, that is, the substrate/transition layer and transition layer/film interface are both There is electron transfer or interaction, indicating that the material i as a transition layer is effective for improving the bonding force of the substrate/film interface, then this material i is selected; otherwise, it is considered that the transition layer cannot effectively improve the substrate/film interface. force, discard the material i.

Other steps and parameters are the same as in the first or second embodiment.

Embodiment 4: The difference between this embodiment and Embodiment 3 is that step 5 is specifically:

Let: z _i =y _i +y′ _i , that is, _zi represents the absolute value of the interatomic chemical bond population at the interface of the substrate/transition layer and the interatomic chemical bond at the transition layer/film interface when the material i is used as the transition layer The sum of the absolute values of the population numbers, calculate the _zi value for the materials selected in step 4, and select the 2 to 3 materials with the highest _zi ranking as the best according to the _zi ranking results from large to small. transition layer material.

Other steps and parameters are the same as in the first, second or third embodiment.

Embodiment 5: The difference between this embodiment and Embodiment 4 is that in step 41), the method for calculating the interface properties of the substrate/transition layer interface is the same as the specific method for calculating the interface properties of the substrate/thin film.

Other steps and parameters are the same as in the first, second, third or fourth embodiment.

Embodiment 6: The difference between this embodiment and Embodiment 5 is that in step 42), the method for calculating the interface properties of the transition layer/thin film interface is the same as the specific method for calculating the interface properties of the substrate/thin film.

Other steps and parameters are the same as in the first, second, third, fourth or fifth embodiment.

Example

Adopt the following examples to verify the beneficial effects of the present invention:

Example 1

The transition layer material selection method based on the evaluation of the bonding force between the transition layer epitaxial film and the substrate described in this embodiment is carried out according to the following steps:

Step 1. Determine the possible selection range of transition layer materials:

For the SiO ₂ (100) (oxidized Si) substrate and the MgO thin film to be prepared, the more commonly used transition layer is the TiN transition layer. In addition, according to the principle described in the literature, other reducing materials can also be considered, such as Ti, TiC, etc.

Step 2: Establish the required interface model;

真空层；21) Construction of SiO ₂ (100)/MgO (100) interface model: The SiO ₂ (100)/MgO (100) interface model was constructed in the Visualizer module of Material Studio. Firstly, two crystal models of SiO ₂ and MgO are established according to the crystal type, space group and lattice constant. When cutting the (100) surface, there are 5 layers of SiO ₂ (100) (including 5 layers of Si atoms and 5 layers of O atoms) and 5 layers of MgO (100) atomic layers, set the top value of SiO ₂ to 0 and the top value of MgO to be 0. 0.5. Expand the surface, for SiO ₂ , set U=V=3, MgO set U=V=5, use Build Layer to connect the two surfaces to form a SiO ₂ (100)/MgO (100) interface model, and then select Build Vacuum Slab as interface model added

vacuum layer;

22) Construction of SiO ₂ (100)/TiN (100) interface model: similar to step 21), establish a TiN crystal model, since the lattice constant of TiN is similar to MgO, the parameters used are the same as in step 21);

23) Construction of the TiN(100)/MgO(100) interface model: In a similar step to step 3.1, the TiN(100)/MgO(100) interface model was established in the Visualizer module of MaterialStudio. Due to the lattice constants of TiN and MgO close, no need to expand the surface to form a supercell, just connect the two surfaces directly;

24) Construction of other interface models: According to the selected transition layer, establish other interface models. For example, when TiC is selected as the transition layer, establish SiO ₂ (100)/TiC(100) and TiC(100)/MgO(100 ) interface model.

Step 3. Calculate the interface properties when there is no transition layer (ie, substrate/film SiO ₂ (100)/MgO (100)), and determine whether a transition layer is required:

31) Geometric optimization and property calculation of the SiO ₂ (100)/MgO(100) interface: The CASTEP module in the Material Studio 8.0 platform was used to optimize the geometry of the established SiO ₂ (100)/MgO(100) interface model and For property calculation, the generalized gradient approximation GGA-PW91 is selected as the exchange correlation function, and the electron-ion interaction is processed by the ultrasoft pseudopotential. The dots are 5×5×1. In the properties, check the density of states (also check the calculation of the partial wave density of states PDOS) and the population analysis (also check the chemical bond population analysis), and run the calculation;

32) Analysis of the interface structure and properties of the SiO ₂ (100)/MgO(100) interface: Select the population analysis in the analysis of the CASTEP module, assign charges and chemical bonds to the structure, and find that the charges of Si and Mg atoms at the interface vary greatly. small (Si5.4%, Mg4.7%, the change rate is less than 10%), and no new chemical bonds are formed at the interface.

33) Determine whether a transition layer is needed: According to the results of steps 31) and 32), it shows that the SiO ₂ (100)/MgO (100) interface has poor bonding force, and a transition layer needs to be added to improve the bonding force.

Step 4. Calculate the interface properties of the substrate/transition layer SiO ₂ (100)/TiN(100) and the transition layer/film TiN(100)/MgO(100), and the combination of the transition layer to the substrate and the transition layer to the thin film Comprehensive evaluation of power:

41) Calculate the interface properties of the SiO ₂ (100)/TiN(100) interface:

411) Geometry optimization: same as step 31);

晶格常数在a、b方向略增加，在c轴方向缩小；Interface structure: After the geometric optimization is completed, the structure of the SiO ₂ (100)/TiN(100) interface is obtained (as shown in Figure 2), in which the atomic distance between Ti-Si and N-Si (the distance between Ti, N atoms and Si atoms) is composed of planes) are

The lattice constant increases slightly in the a and b directions, and decreases in the c-axis direction;

412) Analysis of atomic charge amount and electron transfer at the interface: the method is the same as step 32), and the charge of the atom at the interface is compared with the charge of the atom far away from the interface, and the results are listed in Table 1. The results show that the charge of Ti and Si atoms at the interface has dropped significantly, while the charge of N atom has decreased slightly (the absolute value has increased slightly);

Table 1 SiO ₂ (100)/TiN(100) interface atomic charge and change

element atomic charge at the interface far interface atomic charge Electron transfer direction Ti 0.34 1.21 Greatly↓ N -0.68 -0.65 Small range↓(absolute value↑) Si 1.06 2.40 Greatly↓

413) Analysis of the population number of chemical bonds at the interface: Assign chemical bonds to the structure. In addition to the chemical bonds inside the structure, Si-Ti chemical bonds appear at the interface. The population number is 0.43, showing a relatively strong covalent bond property. long for

414) Analysis of atomic fractional wave density of states at the interface: select Ti, N, Si atoms at the interface respectively, select the density of states and fractional density of states in the analysis of the CASTEP module, and import the results into Origin to re-draw the interface atoms. After comparing the partial wave density of states with the partial wave density of states of atoms far away from the interface, it can be found that the peak of the d-orbital density of states of Ti atoms at the interface at about 3.660 eV is affected by the electronic density of states of the p-orbital electrons of Si atoms; The peak of the p-orbital density of states of the Si atom at the interface around 1.211 eV, as well as the intensity enhancement of several other nearby peaks, are caused by the resonance with the d-orbital electrons of the Ti atom. Atomic s and p orbital electron influence, but extremely weak;

42) Interface properties of TiN(100)/MgO(100) interface:

421) Geometry optimization: the specific operation method is the same as step 31);

Interface structure: After the geometric optimization is completed, the structure of the TiN(100)/MgO(100) interface is obtained (as shown in Figure 3), where the atomic distances of N-Mg and Ti-O are respectively The lattice constant decreases slightly in the a and b directions, and shrinks in the c-axis direction;

422) Analysis of atomic charge and electron transfer at the interface: the specific operation steps are similar to 32), and the charge of the atom at the interface is compared with the charge of the atom far away from the interface, and the results are listed in Table 2. From the analysis of the absolute value of the charge, the absolute value of the charge of the N and Mg atoms at the interface increases, indicating that the charge between the two atoms has been transferred;

Table 2 TiN(100)/MgO(100) interface atomic charge and change

element atomic charge at the interface far interface atomic charge Electron transfer direction O -1.12 -1.23 ↑(absolute value↓) Mg 1.54 1.21 ↑ N -0.83 -0.74 ↓(absolute value↑) Ti 0.43 0.80 ↓

同时出现了具有弱共价键性质的O-Ti键，布居数为0.08，键长为

423) Analysis of the population number of chemical bonds at the interface: The specific steps are similar to 32), except for the chemical bonds inside the structure, N-Mg chemical bonds appear at the interface, and the population number is -0.95, showing relatively strong ionic bond properties, The bond length is

At the same time, O-Ti bonds with weak covalent bond properties appeared, with a population number of 0.08 and a bond length of

424) Analysis of the atomic fractional wave density of states at the interface: The specific steps are similar to 414). After comparing with the fractional density of states of atoms far away from the interface, it can be found that the p-orbital density of states of the Mg atom at the interface appears around -15.422 eV. The peak is affected by the density of electron states of the s orbital electrons of the N atom; the intensity of the peak intensity of the p orbital state density of the N atom at the interface around -4.929 eV is the result of resonance with the electrons of the p orbital electrons of the Mg atom;

42) Functional evaluation of the TiN transition layer: According to the simulation results, the TiN transition layer can significantly improve the bonding force of the MgO(100) thin film on the Si(100) substrate. The TiN transition layer plays a linking role in the whole structure. On the one hand, between it and the SiO ₂ oxide layer on the surface of the oxidized silicon substrate, a bonding form similar to Ti-Si covalent bond is formed, and N-Si The ionic bond-like bond form is the auxiliary bond (the interatomic chemical bond population at the interface is 0.43, greater than 0.10); on the other hand, with the metal oxide film MgO, an N-Mg-like ionic bond form (net The change in charge amount is Mg21.4%, N10.8%, more than 10%, and the absolute value of the interatomic chemical bond population at the interface is 0.95, which is greater than 0.10), thereby improving the bonding force of the entire structure.

Step 5. Select the appropriate transition layer:

The properties of the Ti and TiC transition layers were simulated and evaluated according to step 4, and the TiN transition layer was finally selected as the transition layer material between the SiO ₂ substrate and the MgO thin film.

Step 6. Prepare actual SiO ₂ (100)/MgO(100) and SiO ₂ (100)/TiN(100)/MgO(100) samples, and test their properties:

61) Preparation of epitaxial samples:

611) Surface treatment of oxidized Si(100) substrate (SiO ₂ (100)): the Si(100) substrate is cut into wafers with a size of 12mm × 7mm with a glass knife, and treated in acetone, absolute ethanol, deionized water Each ultrasonic cleaning was performed for 5 min each.

The substrate was immersed in a solution with a volume ratio of H ₂ O ₂ : deionized water = 1:20, the water bath was kept at 65° C., and pre-oxidized for 10 minutes; the immersion volume ratio was NH ₄ OH: H ₂ O ₂ : deionized water = 1: In the SC-1 solution of 1:10, the water bath was heated to 65 ℃, and the heat preservation treatment was carried out for 10 minutes; after deionized water was rinsed, immersed in the SC-2 solution with a volume ratio of HCl:H2O2:deionized water=1:1:6, Heated to 65 °C for 10 min, and rinsed with deionized water. Immerse in a DHF solution with a volume ratio of HF:deionized water=1:5, place at room temperature for 15 min to remove the oxide layer on the surface of the substrate, ultrasonically treat with absolute ethanol for 5 min, and store the treated substrate in absolute ethanol;

612) Growth of TiN(100) transition layer on oxidized Si(100) substrate (SiO ₂ (100)): The TiN(100) transition layer was deposited in a pulsed laser deposition system (PLD) that simultaneously 6 targets are installed to realize the target revolution switching, and a shielding cover shields the targets not used for deposition to avoid the contamination of the film. A high-purity TiN target (99.95%) was selected as the raw material to grow the TiN epitaxial film, and the MgO target was also pre-installed on the target assembly. The entire deposition process was carried out under vacuum conditions, and the substrate temperature was set to 550 °C, the laser intensity was 3 J/cm ² , the laser frequency was 10 Hz, the target-to-base distance was 4.5 cm, and the deposition time was 30 min;

613) Growth of MgO(100) epitaxial layer: The TiN target was switched to a high-purity MgO target (99.95%) to prepare a MgO(100) thin film. The vacuum conditions of the growth chamber were maintained, the substrate temperature was 700 °C, the laser intensity was 5 J/cm ² , the laser frequency was 10 Hz, the target-to-base distance was 4 cm, and the deposition time was 90 min;

614) Preparation of SiO ₂ (100)/MgO (100) samples: the Si (100) substrate is treated by the same method as in step 611), and a MgO (100) film is prepared on the substrate by the same method as in step 613), as Test comparative samples.

62) X-ray photoelectron spectroscopy (XPS) test of SiO ₂ (100)/MgO(100) and SiO ₂ (100)/TiN(100)/MgO(100) samples: for SiO ₂ (100)/TiN(100 )/MgO(100) samples were etched, and X-ray photoelectron spectroscopy tests were performed at the interfaces of SiO ₂ (100)/TiN(100) and TiN(100)/MgO(100), respectively. The splitting results of the Ti1/2p peak at the SiO ₂ (100)/TiN(100) interface of this sample indicate that a chemical bond similar to the Si-Ti bond with energy close to TiSi ₂ is formed at the interface (as shown in Figure 4). ), it can be seen that there is a small chemical bond effect similar to Si-N bond with energy close to Si ₃ N ₄ by dividing the peak of N1s, but this is not the main mode of action. The splitting results of the Mg1s peak at the TiN(100)/MgO(100) interface indicate that a chemical bond similar to Mg-N bond with energy close to Mg ₃ N ₂ is formed at the interface (as shown in Figure 5). The atoms at the interface of SiO ₂ (100)/MgO(100) samples did not show similar chemical bond results;

63) Nano scratch test of SiO ₂ (100)/MgO(100) and SiO ₂ (100)/TiN(100)/MgO(100) samples:

631) Nano-scratch test of SiO ₂ (100)/TiN(100)/MgO(100) samples: the scratch depth increased from 10nm to 30nm, under scanning electron microscope, no film peeling or peeling was observed. , indicating that the film and the substrate are well combined;

632) Nano-scratch test of SiO ₂ (100)/MgO(100) samples: when the scratch depth is less than 15nm, no film peeling is observed under the scanning electron microscope. The peeling phenomenon of the thin film was observed under the microscope (as shown in Figure 6), indicating that the bonding of the thin film and the substrate was poor.

Example 2

An example of the transition layer selection based on the evaluation of the effect of the transition layer on the bonding force between the epitaxial YSZ (yttrium stabilized zirconia) thin film and the oxidized Si substrate (SiO ₂ (100)), which is the same as or similar to other steps in Example 1, only Step 6 was replaced with the following steps: YSZ thin films were prepared on Si(100)/TiN(100) by pulsed laser deposition (PLD). The targets were pre-fired with ZrO ₂ and Y ₂ O ₃ ceramic powders, and then ball-milled with different mass ratios (the mass ratios of ZrO ₂ and Y ₂ O ₃ ceramic powders were 100:8, 100:11, and 100:15, respectively). Firing at 1500°C, tablet pressing, and hot pressing to finally form a circular target with a diameter of 25mm. During deposition, O ₂ was introduced as a background gas with a pressure of 0.01 Pa, a substrate temperature of 700-750 °C, a laser energy of 5 J/cm ² , a laser frequency of 10 Hz, a target-to-base distance of 4 cm, and a deposition time of about 50 min. In this structure, through the simulations in steps 1 to 5, TiN(100) is still the most suitable transition layer material, and the bonding force between it and the YSZ(100) thin film is N-Zr (N-metal in metal oxides) elements) similar to chemical bonds.

Example 3

An example of selection of transition layer based on the evaluation of the effect of transition layer on the bonding force between the epitaxial SrTiO ₃ film and the oxidized Si substrate (SiO ₂ (100)), the same or similar to other steps in Example 1, only the following steps are used instead of steps Six: Use two high-purity targets, SrO and TiO ₂ , and put them into the growth chamber of the pulsed laser deposition system (PLD) together with the TiN target. When depositing the SrTiO ₃ film, cover the substrate every 2min, and then pass the target The material revolution rod is used, and SrO and TiO ₂ targets are selected in turn, and the layers are deposited, and the SrTiO ₃ film is formed by their reaction. The deposition conditions were substrate temperature of 800-850° C., laser energy of 5 J/cm ² , laser frequency of 10 Hz, target base distance of 4 cm, and deposition time of about 50 min. In this structure, through the simulation in steps 1 to 5, TiN(100) is still the most suitable transition layer material, and the bonding force between it and SrTiO ₃ (100) thin film is N-Sr and N-Ti(N-metal similar chemical bonding of metal elements in oxides).

The present invention can also have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations are all It should belong to the protection scope of the appended claims of the present invention.

Claims (4)

1. The transition layer material selection method based on the evaluation of the bonding force between the epitaxial film and the substrate of the transition layer, the transition layer material selection method based on the evaluation of the bonding force between the transition layer epitaxial film and the substrate specifically comprises the following steps: Step 1: Select several transition layer materials according to the properties of the substrate material and the film material; Step 2. Establish the required interface model; the specific process includes: 21) According to the lattice constant and lattice type of the crystal, respectively establish the crystal model of the substrate material, the transition layer material and the thin film material; 22) Based on the crystal model, the surface models of the substrate material, the transition layer material and the thin film material are established respectively according to the crystal plane index, the thickness and direction parameters of the surface are adjusted, and the supercell is established according to the lattice constant, so that the surfaces that will be combined into the interface are formed. The lattice constants of the surfaces of the two materials differ by less than 5%; 23) Combine the constructed surface models into substrate/film, substrate/transition layer, transition layer/film interface models, and add a thickness not less than

the vacuum layer to form crystals; Step 3: Calculate the interface properties when there is no transition layer, that is, the interface properties of the substrate/film. According to the change in the net charge at the interface and the number of interatomic chemical bonds, determine whether a transition layer is required; if a transition layer is required, carry out Step four; The specific calculation steps of the interface properties of the substrate/film include: 31) Geometric optimization and property calculation of the substrate/thin film interface: Use the CASTEP module in the Material Studio material calculation software to perform geometric optimization and property calculation of the substrate/thin film interface, select the exchange correlation function and pseudopotential, and select the "geometric optimization". "task, get the structure of the substrate/film interface; set the accuracy, cut-off energy, and k-point value according to the size of the model, select the change in net charge and the number of chemical bonds between atoms in the Properties tab, and run the calculation; 32) Analysis of atomic charge and electron transfer at the interface: select the population analysis in the analysis of the CASTEP module, select the calculated .castep file as the result file, choose to assign the charge to the structure, and mark the charge after the geometry optimization. On each atom of the model of , compare the charge of atoms at the interface with the charge of atoms far away from the interface to obtain the net charge change at the substrate/film interface; 33) Analysis of the chemical bond population at the interface: in the population analysis, choose to assign chemical bonds to the structure, and obtain the interatomic chemical bond population at the substrate/film interface. The positive and negative signs of the population indicate the type of interaction, and a positive value Represents a covalent bond, a negative value represents an ionic bond, and the absolute value indicates the relative strength of the interaction force; Step 4: Calculate the interface properties of the substrate/transition layer and the transition layer/thin film when the material within the range selected in Step 1 is used as the transition layer, and according to the change in the net charge at the interface and the number of interatomic chemical bonds, for When different materials are used as the transition layer, the transition layer comprehensively evaluates the bonding force of the substrate and the transition layer to the film, and selects the material that is effective for improving the bonding force of the substrate/film interface; Step 5: Evaluate and sort the bonding force between the film and the substrate when the material selected in Step 4 is used as the transition layer; select the first 2 to 3 transition layer materials according to the sorting result; It is characterized in that, the method for determining whether a transition layer is required in step 3 is: According to the calculation results of the interface properties when there is no transition layer in step 3, determine whether a transition layer is required; if the change in the net charge between atoms at the interface is less than 10% and the absolute value of the population of chemical bonds between atoms at the interface is less than 0.10, it is necessary to A transition layer is introduced to improve the interfacial bonding force between the film and the substrate, otherwise the transition layer is not required; In step 4, the specific steps of comprehensively evaluating any material within the range selected in step 1 include: For any material i within the range selected in step 1 as the transition layer: 41) Calculate the interface properties of the substrate/transition layer interface, and obtain the net charge amount change x _i at the substrate/transition layer interface and the absolute value y _i of the population of chemical bonds between atoms at the substrate/transition layer interface; Calculate the interface properties of the transition layer/film interface, and obtain the net charge change x' _i of the transition layer/film interface and the absolute value of the interatomic chemical bond population y' _i at the transition layer/film interface; 42) Functional evaluation of transition layer: if x _i ≥ 10% or y _i ≥ 0.10, and at the same time x' _i ≥ 10% or y' _i ≥ 0.10, then select this kind of material i, otherwise, discard this kind of material i . 2. the transition layer material selection method based on the transition layer epitaxial film and substrate bonding force evaluation according to claim 1, is characterized in that, step 5 is specifically: Let: _zi = y _i +y′ _i , calculate the value of _zi for the effective materials in step 4, and select the first 2 to 3 materials corresponding to _zi according to the sorting result of _zi from large to small as Optimum transition layer material. 3. the transition layer material selection method based on the transition layer epitaxial film and the substrate bonding force evaluation according to claim 2, is characterized in that, in step 41), the interface property calculation method of substrate/transition layer interface is the same as the described method. The specific calculation method for the interface properties of the substrate/thin film is the same. 4. the transition layer material selection method based on the evaluation of the transition layer epitaxial film and the substrate binding force according to claim 3, is characterized in that, in step 42), the interface property calculation method of transition layer/film interface and described lining The specific calculation method for the interface properties of the substrate/film is the same.

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