CN101174671A - Preparation method of vanadium dioxide nano film with phase change characteristics - Google Patents

Abstract

The invention belongs to the technical field of semiconductors, and in particular relates to a preparation method for preparing a vanadium dioxide nano-film with a phase change characteristic, which is used for making a vanadium dioxide nano-film on a silicon substrate, comprising the following steps: 1) cleaning the surface of the silicon substrate; 2) using plasma-enhanced chemical vapor deposition method to grow a silicon dioxide film or a silicon nitride film on a silicon substrate; 3) using metal vanadium as a target material, using a reactive magnetron sputtering method to the target, on the above-mentioned silicon dioxide/ Deposit vanadium oxide thin film on silicon substrate or silicon nitride/silicon substrate; In the annealing device with high temperature, the annealing is carried out under the air atmosphere, the annealing temperature is 300-400° C., and the annealing time is 1-3 hours. In the preparation method provided by the invention, the film sputtering temperature is room temperature, and the annealing temperature is very low, the lowest being only about 300°C. The vanadium dioxide nano film prepared by this method has good phase transition characteristics and is very compatible with MEMS technology. good.

Description

Preparation method of vanadium dioxide nano film with phase change characteristics

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a preparation method for preparing vanadium dioxide nano-films with phase transition properties.

Background technique

Vanadium dioxide is a thermally induced phase-change material, which changes from a low-temperature semiconductor state to a high-temperature metal state in the process of temperature rise, and at the same time, the crystal structure changes from a monoclinic rutile structure to a tetragonal rutile structure. During the phase transition, the optical, electrical and magnetic properties of vanadium dioxide undergo reversible mutations. This feature makes it widely used in photoelectric switch, optical memory, smart window coating and other fields. Normally, the phase transition temperature of vanadium dioxide polycrystalline film is 68°C the same as that of the bulk material. Near the phase transition temperature, the temperature coefficient of resistance is much larger than the values in other temperature regions. The phase transition temperature can be changed by doping or changing the process. The method of condition is effectively reduced, so that the region of high temperature coefficient of resistance moves to the region of low temperature, and the appropriate resistivity makes it also an ideal heat-sensitive element material for uncooled microbolometers. To achieve a better application of vanadium dioxide thin film in the above fields, in addition to the pursuit of low phase transition temperature, high phase transition amplitude, high temperature coefficient of resistance and suitable resistivity, when preparing vanadium dioxide thin film, its preparation process and micro The compatibility issue of the mechatronics system (MEMS) process is also crucial, the most important thing is that the preparation temperature should not exceed 450°C. At present, when preparing vanadium dioxide thin films, the annealing temperature is generally 400°C, sometimes even above 500°C. For example, the patent application whose application number is 200510039179.2 provides a method for preparing a polycrystalline vanadium dioxide thin film with a temperature coefficient of resistance at room temperature higher than 10%/K (the unit of temperature coefficient of resistance). The annealing temperature used in this preparation method is as high as 500 -700°C. If the preparation temperature of vanadium dioxide film is too high, it is easy to damage the existing circuit and microstructure on the substrate, thereby limiting the application of vanadium dioxide in the above fields. Therefore, the low preparation temperature of vanadium dioxide film with good performance becomes its Necessary for the above application.

Contents of the invention

The purpose of the present invention is to provide a low-temperature oxidation annealing method for preparing vanadium dioxide nano-films with phase transition characteristics. The main features of this method are that the film sputtering temperature is room temperature, and the annealing temperature is very low, the lowest being only about 300 ° C. The vanadium dioxide nanometer thin film prepared by the method has good phase transition properties, and has good compatibility with MEMS technology.

The low-temperature annealing preparation method of the vanadium dioxide nano-film with phase change characteristics of the present invention is used to make the vanadium dioxide nano-film on a silicon substrate, comprising the following steps:

1) Silicon substrate surface cleaning;

2) growing a silicon dioxide film or a silicon nitride film on a silicon substrate by a plasma-enhanced chemical vapor deposition method;

3) Depositing a vanadium oxide film on the above-mentioned silicon dioxide/silicon substrate or silicon nitride/silicon substrate by using metal vanadium as the target material and adopting a reactive magnetron sputtering method to the target;

4) Place the prepared vanadium oxide/silicon dioxide/silicon composite film or vanadium oxide/silicon nitride/silicon composite film in an annealing device that has reached the required annealing temperature, and perform annealing in an air atmosphere at an annealing temperature of 300-400°C, the annealing time is 1-3 hours.

As a preferred embodiment, step 2) in the above preparation method can adopt the following steps: first place the processed silicon substrate in a vacuum chamber, the temperature of the substrate is 130°C-160°C, the working gas is NO ₂ and SiH ₄ , The working gas pressure is 3-5Pa, the gas flow ratio is 1:2 to 1:3, and the deposition time is 10-15 minutes; the process condition of magnetron sputtering for target reaction in step 3) can be: background vacuum degree To (2-3)×10 ^-4 Pa, the working gas is oxygen and argon, the gas flow ratio is 49.2ml/min: 0.8ml/min～48.8: 1.2ml/min, the working pressure during sputtering is 1 -2Pa, the power used is 200-220W, and the sputtering time is 3-10 minutes; after step 4), a step of sputtering metal electrodes at both ends of the vanadium oxide film may also be included.

Technical effect of the present invention is as follows:

1) In the present invention, the preparation of the vanadium oxide film does not need to increase the substrate temperature, and after low-temperature annealing (the lowest temperature can be 300 ° C), the vanadium oxide film can be changed into a vanadium dioxide nanometer with good phase transition characteristics. Thin films, improving compatibility with MEMS processes.

2) The phase transition temperature of the vanadium dioxide nano-film with phase transition properties prepared on silicon dioxide/silicon substrate or silicon nitride/silicon substrate by the present invention is reduced to 45°C, which is lower than the phase transition temperature of vanadium dioxide by 68°C. ℃.

Description of drawings

Fig. 1 is a schematic structural view of a vanadium oxide thin film on a silicon substrate of the present invention. In the figure: 1 is a silicon substrate, 2 is a silicon dioxide layer, and 3 is a vanadium oxide film layer;

Fig. 2 is the graph that the resistance of the low-temperature oxidized vanadium dioxide thin film that embodiment 1 makes changes with temperature;

Fig. 3 is the X-ray diffraction (XRD) pattern of vanadium dioxide film after 300 ℃ of low-temperature oxidation annealings;

Figure 4 is the surface morphology of the vanadium dioxide film after low temperature oxidation annealing at 300°C;

Fig. 5 is the graph that the resistance of the low-temperature oxidized vanadium dioxide thin film that embodiment 2 makes changes with temperature;

FIG. 6 is a graph showing the variation of the resistance of the low-temperature vanadium dioxide film prepared in Example 3 as a function of temperature.

Detailed ways

The invention provides a method for preparing a vanadium dioxide nano-film with phase transition properties on a silicon substrate, which mainly includes the following steps:

1) Silicon substrate surface cleaning, using standard semiconductor cleaning process;

2) growing a silicon dioxide film on a silicon substrate by plasma-enhanced chemical vapor deposition;

3) The vanadium oxide thin film is deposited on the silicon dioxide/silicon substrate by using the reactive magnetron sputtering method to the target, and the process condition of the reactive magnetron sputtering to the target is: the background vacuum degree is (2-3)×10 ^{− 4} Pa, the working pressure during sputtering is 1-2Pa, the power used is 200-220W, the sputtering time is 3-10 minutes, and the gas flow rates of Ar and _O2 are 49ml/min and 1ml/min respectively;

4) The prepared vanadium oxide/silicon dioxide/silicon composite film is placed in an annealing device that has reached the required annealing temperature, and annealed in an air atmosphere. The annealing temperature is 300-400 ° C, and the annealing time is 1-3 hours , so as to obtain a vanadium dioxide film with good performance and phase change characteristics;

5) Sputtering metal electrodes on both ends of the vanadium oxide film.

The present invention will be described in further detail below in conjunction with the embodiments and accompanying drawings.

Example 1

1) Using a p-type (100) single-sided polished single-crystal silicon wafer with a thickness of 380-420 μm, a length of 2.5 cm, and a width of 1 cm as a substrate, the surface of the silicon substrate is treated as follows: take _H2 with a mass concentration of 98% 30 milliliters of SO ₄ and 10 milliliters of H ₂ O ₂ with a mass concentration of 30% were used as a cleaning solution, and the silicon wafer was put into the cleaning solution, soaked at room temperature, and left for 40 minutes to remove organic pollutants on the surface; After the silicon chip is taken out from the mixed acid, it is rinsed with deionized water for 3 times, and then immersed in a HF solution with a volume of 30 ml and a mass concentration of 20% for 30 seconds to remove the oxide layer on the surface; and then rinsed with deionized water; Place the silicon wafer in an acetone solution with a volume of 20 ml and ultrasonically clean it for 5 minutes; take out the silicon wafer and put it into anhydrous ethanol with a volume of 20 ml for ultrasonic cleaning for 5 minutes; take out the silicon wafer and dry it for later use; Chemical vapor deposition (PECVD) method first deposits a layer of silicon dioxide film on the silicon substrate. The specific method is: first place the processed silicon in a vacuum chamber, pump the background vacuum to 4.5×10 ^-1 Pa, and use the working gas The pressure is 4.3Pa, the substrate temperature is 150°C, the working gas is NO ₂ and SiH ₄ , the gas flow is 12ml/min and 38ml/min respectively, the deposition time is 10 minutes, and the obtained SiO ₂ layer has a thickness of 1000 Ȧ; The vanadium oxide thin film is prepared on the above-mentioned silicon substrate with silicon dioxide by DC reactive magnetron sputtering method, and the metal vanadium with a mass purity of 99.9% is used as the target material, and the mass purity of argon and oxygen are respectively 99.999% And 99.995%, the specific steps of magnetron sputtering for the target reaction are: pump the background vacuum to 2×10 ^-4 Pa, the flow ratio of oxygen and argon is 49ml/min: 1ml/min, the sputtering pressure is 1Pa, sputtering The power is 210W, the sputtering time is 5 minutes, the substrate temperature is room temperature, and a vanadium oxide film layer with a length of 2 cm and a width of 0.2 cm is obtained; the above vanadium oxide film is placed in an annealing device and kept at 300 ° C for 1 hour; The above-mentioned vanadium dioxide film was tested for resistance-temperature characteristics. The temperature range is 20-80°C. The resistance-temperature curve is shown in Figure 2. The phase transition temperature of the vanadium dioxide film is 45°C, and the phase transition range is greater than 1 order of magnitude.

In this embodiment, the process step of depositing a silicon dioxide film on a silicon substrate by using the plasma chemical vapor deposition (PECVD) method can adopt conventional process conditions, such as working gas pressure and flow ratio, silicon substrate temperature, Process conditions such as deposition time may vary.

Example 2

This embodiment is similar to Embodiment 1, except that the annealing temperature is 320° C. in the process parameters of vanadium oxide annealing in step 4, the annealing time is 3 hours, and the phase transition temperature of the obtained vanadium dioxide film is 43° C. The magnitude of the phase change is greater than 1 order of magnitude; the resistance temperature curve is shown in Figure 5.

Example 3

This embodiment is similar to Embodiment 1, except that the annealing temperature is 360° C. in the process parameters of vanadium oxide annealing in step 4, the annealing time is 1 hour, and the phase transition temperature of the obtained vanadium dioxide film is 40° C. The magnitude of the phase change is greater than 1 order of magnitude; the resistance temperature curve is shown in Figure 6.

Example 4

The difference between this embodiment and embodiment 1 is that in embodiment 1, a layer of silicon dioxide film is first deposited on the cleaned silicon substrate, while in this embodiment, plasma chemical vapor deposition (PECVD) is used. Methods First deposit a layer of silicon nitride film on the silicon substrate. The specific method is: first place the processed silicon in a vacuum chamber, pump the background vacuum to 4.5×10 ^-1 Pa, and the working gas pressure is 4.3Pa. The temperature is 150°C, the working gas is NH ₃ and SiH ₄ , the gas flow is 14ml/min and 40ml/min respectively, the deposition time is 15 minutes, and the thickness of the obtained silicon nitride layer is 1000 Ȧ. Other process conditions and examples 1 is similar.

Example 5

This embodiment is similar to embodiment 4, except that: the annealing temperature is 320° C., and the annealing time is 3 hours in the process parameters of vanadium oxide annealing in step 4.

Example 6

This embodiment is similar to Embodiment 4, except that the annealing temperature is 360° C. and the annealing time is 1 hour in the process parameters of vanadium oxide annealing in step 4.

The inventors analyzed the composition, surface morphology and thermal properties of the vanadium oxide film prepared by the method. The cross-sectional view of the produced film structure is shown in Figure 1; the resistance value of the deposited vanadium oxide film was measured in the temperature range of 25-80 °C after annealing, as shown in Figure 2; the crystallographic orientation of the vanadium oxide film after annealing And component analysis, as shown in Figure 3, the film is dominated by vanadium dioxide; the field emission scanning electron microscope photo of the vanadium oxide film after annealing, as shown in Figure 4, it can be seen from the photo that the particle size is 20-40nm; Figure 5 and Figure 6 are the relationship curves of the resistance and temperature of the obtained vanadium dioxide film at the annealing temperature of 320°C and 360°C respectively.

Comparing Figure 2, Figure 5, and Figure 6, it can be seen that after annealing at 300°C, 320°C, and 360°C, vanadium oxide films have obtained vanadium dioxide nano-films with phase transition characteristics, which shows that the use of direct current to the target magnetron The vanadium oxide thin film is prepared at room temperature by the sputtering method, and the vanadium dioxide nano thin film with high-performance phase change characteristics can be obtained after low-temperature annealing at 300°C, and the compatibility with the MEMS process is improved.

Claims (4)

1. a kind of preparation method with phase-change characteristic vanadium dioxide nano-film is used for making vanadium dioxide nano-film on silicon substrate, it is characterized in that comprising the following steps: 1) Silicon substrate surface cleaning; 2) growing a silicon dioxide film or a silicon nitride film on a silicon substrate by a plasma-enhanced chemical vapor deposition method; 3) Depositing a vanadium oxide film on the above-mentioned silicon dioxide/silicon substrate or silicon nitride/silicon substrate by using metal vanadium as the target material and adopting a reactive magnetron sputtering method to the target; 4) Place the prepared vanadium oxide/silicon dioxide/silicon composite film or vanadium oxide/silicon nitride/silicon composite film in an annealing device that has reached the required annealing temperature, and perform annealing in an air atmosphere at an annealing temperature of 300-400°C, the annealing time is 1-3 hours. 2. the preparation method with phase-change characteristic vanadium dioxide nano film according to claim 1, is characterized in that, step 2) comprises the following steps: earlier silicon substrate processed is placed in vacuum chamber, and substrate temperature is 130°C-160°C, the working gas is NO ₂ and SiH ₄ , the working gas pressure is 3-5Pa, the gas flow ratio is 1:2-1:3, and the deposition time is 10-15 minutes. 3. the preparation method with phase-change characteristic vanadium dioxide nano film according to claim 1, is characterized in that, in step 3) to target reactive magnetron sputtering process condition is: pumping background vacuum degree to (2- 3)×10 ^-4 Pa, the working gas is oxygen and argon, the gas flow ratio is 49.2ml/min:0.8ml/min～48.8:1.2ml/min, the working pressure during sputtering is 1-2Pa, the used The power is 200-220W, and the sputtering time is 3-10 minutes. 4. The preparation method of vanadium dioxide nano-film with phase-change characteristics according to claim 1, characterized in that, after step 4), the step of sputtering metal electrodes at both ends of the vanadium oxide film is also included.

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