CN101153379A - Preparation method of transparent MgO thin film and product obtained therefrom - Google Patents

Abstract

The invention discloses a method for preparing a transparent MgO thin film by means of an arc ion plating method. The method comprises: placing a substrate in a vacuum chamber, the vacuum chamber is connected to the positive pole of a low-voltage high-current DC power supply, and pure magnesium is used as a cathode target, and the cathode target is It is connected to the negative pole of the low-voltage high-current DC power supply; Ar gas is introduced into the vacuum chamber, and the plasma generated by Ar gas glow discharge under high bias is used to bombard and clean the substrate surface; after the bombardment cleaning is completed, the vacuum chamber is fed The reaction gas O ₂ and the protective gas Ar make the working pressure in the vacuum chamber 0.2-4Pa; and apply a negative bias voltage to the substrate and ignite the arc for coating.

Description

Preparation method of transparent MgO thin film and product obtained therefrom

technical field

The invention relates to a preparation method of MgO thin film and the obtained product, in particular to a preparation method of transparent MgO thin film and the obtained product.

Background technique

At present, MgO (magnesium oxide) functional thin film as a dielectric protective layer of color plasma display has aroused people's widespread interest and has been practically applied. In the prior art, the main preparation methods of MgO thin films include electron beam evaporation and magnetron sputtering.

Among them, the electron beam evaporation method uses pure MgO as the evaporation material, and uses electron beam focused heating to evaporate MgO. However, there are many voids in the film prepared by this method, the film is not firmly bonded to the substrate, and it is easy to crack during the annealing process.

Among them, the magnetron sputtering method has two kinds of direct current and radio frequency magnetron sputtering. DC magnetron sputtering uses metal magnesium as the target, and at the same time, the reaction gas O ₂ is introduced, and the plasma generated by the glow discharge of Ar gas is used to bombard the target surface, thereby sputtering out magnesium ions (atoms) and reacting with O ₂ to form MgO; RF magnetron sputtering generally uses pure MgO as the target material, the target surface is bombarded by Ar ⁺ ions, and the sputtered MgO molecules are deposited on the substrate to form a MgO film. However, the deposition rate of magnetron sputtering is too low, which greatly limits its industrial application.

In recent years, some people have introduced arc ion plating technology into the preparation process of MgO thin film. At the end of 2004, Kim et al. from South Korea published an article on Thin Solid Films, introducing that the MgO film prepared by arc ion plating technology has the characteristics of high density and strong plasma bombardment resistance. However, this article does not disclose the effects of process parameters, such as substrate bias voltage and reactive gas partial pressure, on the structure and performance of MgO thin films. Therefore, those skilled in the art cannot prepare the MgO thin film described in this article, and cannot obtain the inspiration for preparing the MgO thin film described in this article.

Another example is a MgO thin film preparation process disclosed in Chinese Patent No. 01133479.7. It adopts a multi-arc ion plating method, uses pure Mg as a cathode target, and connects the anode to a vacuum chamber. The cathode and anode are respectively connected to a low-voltage, high-current DC power supply. Negative and positive electrodes; before loading the furnace, clean the substrate with HF acid, after loading the furnace, pump the vacuum to 8×10 ^-3 ~ 2.0×10 ^-2 Pa, feed Ar gas and H ₂ , and increase the bias voltage 500~ 700V, use glow discharge to bombard the surface of the substrate, the bombardment time is 3-5min, use _O2 as the reaction gas, use Ar gas as the protective gas, the oxygen flow rate is 160-270Sccm, and the end of the copper air tube of Ar gas It is made into a circle, its size is slightly larger than the Mg target, and it is close to the Mg target, while the gas guide tube for _O2 is close to the substrate, and the arc plating is started by the contact short circuit method, the arc current is 20-40A, and the arc voltage is 20-40A. It is 15V～40V, and the working pressure is 2.0～8.0×10 ^-1 Pa. However, the preparation technology and process parameters disclosed in Chinese Patent No. 01133479.7 have the following problems.

(This paragraph is deleted) First of all, in the actual production process, the MgO thin film prepared by using the working pressure of 10 ^-1 Pa level disclosed in Chinese Patent No. 01133479.7 is not firmly bonded to the substrate, and it is easy to fall off from the substrate , causing the plasma display device to not work stably, bringing additional troubles to both the manufacturer and the user; at the same time, the MgO film prepared with a lower working pressure of 10 ^-1 Pa often fails due to insufficient O ₂ What makes the surface of the substrate is not a MgO film, but a Mg film, like a mirror, cannot be used in a plasma display device, making all the work in vain, wasting manpower and resources; even at a working pressure of 10 ^-1 Pa The prepared MgO film will also contain more Mg impurities in the MgO film, so that the transparency of the MgO film will ^be greatly reduced, and it cannot be applied to actual products; The MgO thin film is not dense enough, so its bombardment resistance is weak and its service life is not long enough; moreover, the emission coefficient of secondary electrons of the MgO thin film prepared under the working pressure of 10 ^-1 Pa level is small, and it is not easy to ignite, thus The ignition voltage of the drive circuit must be a relatively high voltage, and the high operating voltage will eventually lead to a shortened service life of the drive circuit.

In the preparation technology disclosed in Chinese Patent No. 01133479.7, there is no substrate negative bias technology, and the energy of incident ions can hardly be adjusted, so that the purpose of controlling the preferred crystallographic orientation by changing the incident energy cannot be achieved. Films with different crystallographic orientations, Their secondary electron emission coefficients are different. The MgO thin film prepared by the inventor without substrate negative bias, the scanning electron microscope observed that the crystal grains on the surface of the thin film are relatively loose, which will reduce the plasma bombardment resistance of the thin film and is easy to hydrolyze. The inventors used the substrate negative bias technology to change the energy of incident ions to obtain dense films with different preferred crystallographic orientations, thereby realizing the controllable preferred crystallographic orientation of the film, enhanced plasma bombardment resistance and secondary electron emission coefficient of the film. purpose of improvement.

Furthermore, when cleaning the substrate, what Chinese Patent No. 01133479.7 uses is HF acid. This highly corrosive cleaning agent will cause the surface of the glass substrate to be rough, thereby affecting the transparency of the glass. However, as a display device, The higher the transparency requirement, the better. Therefore, the MgO thin film prepared in the above-mentioned patent may have little effect on optimizing the performance of the plasma display device.

In addition, Chinese Patent No. 01133479.7 introduced Ar gas and H ₂ when bombarding the surface of the substrate. However, experiments have shown that high-quality MgO films can also be prepared without feeding H 2 . Therefore, this part of the process for preparing H ₂ Costs can be saved.

In addition, experiments by the inventors have proved that the application of magnetic filtration technology in the arc ion plating technology can effectively reduce the degree of contamination by large particles on the surface of the film. However, so far, there has been no report on the preparation of MgO functional thin films by magnetic filter cathodic arc ion plating technology.

Therefore, it is necessary to provide a high density, high transparency, high secondary electron emission coefficient, stable combination with the substrate, controllable crystal orientation and composition, long service life, low cost, and can be used at room temperature. MgO functional thin films and their preparation methods that can be deposited rapidly under the environment, have less contamination by large particles on the surface, and can be practically applied to plasma display devices have become problems that need to be solved in the industry.

Contents of the invention

The object of the present invention is to provide a method for preparing MgO thin films with dense film layers, firm bonding with the substrate, high transparency, high secondary electron emission coefficient, controllable crystal orientation and composition, and the MgO film prepared by this method. MgO film.

A solution of the present invention is to provide a method for preparing a transparent MgO film by arc ion plating, the method comprising: placing the substrate in a vacuum chamber, the vacuum chamber is connected to the positive electrode of a low-voltage high-current DC power supply, and pure magnesium is used as the The cathode target, the cathode target is connected to the negative electrode of the low-voltage high-current DC power supply; Ar gas is introduced into the vacuum chamber, and a high bias voltage is applied to the substrate to use the plasma generated by Ar gas glow discharge to bombard and clean the substrate surface; After the bombardment cleaning is completed, the reaction gas _O2 and the protective gas Ar are introduced into the vacuum chamber, so that the working pressure in the vacuum chamber is 0.2-4Pa; and a negative bias is applied to the substrate and an arc is ignited to start coating.

Wherein, the negative bias voltage is a pulse bias voltage. For example: the negative bias voltage is 0-1000V, and the duty cycle is 3%-20%;

Before bombardment cleaning, ^the substrate was ultrasonically ^cleaned with ethanol for more than 3 minutes, dried and fixed on the substrate holder in the vacuum chamber. 0.5-3.5Pa, the applied high bias voltage is a pulse bias voltage of 400-1100V, the duty ratio is 3%-20%, and the bombardment cleaning time is 5-20 minutes.

When no magnetic filter is used, the substrate is placed against the cathode target. The flow rate of the reaction gas _O2 introduced into the vacuum chamber is 50-260 sccm, the working pressure in the vacuum chamber during coating is 0.2-4Pa, and the arc current is 45-100A. Specifically, the working air pressure above 1Pa can be selected.

Alternatively, the present invention further adopts a magnetic filter device, the cathode target is installed at one end of the magnetic filter device, and the other end of the magnetic filter device is connected to the vacuum chamber as an ion outlet. The flow rate of the reaction gas _O2 introduced into the vacuum chamber is 5-100 sccm, the working pressure in the vacuum chamber during coating is 0.2-0.8 Pa, and the arc current is 15-80A. The central magnetic field strength of the magnetic filter elbow of the magnetic filter device is 5-15mT. The film prepared by using the magnetic filter device has no or less large particle pollution on its surface, the particle size is less than 600nm, and the particle coverage rate on the film surface is less than 0.5%.

Wherein, the substrate can be a glass slide, a silicon wafer or a stainless steel wafer.

The cathode target is made of high-purity magnesium, and the deposition time during coating is 5 to 30 minutes.

The present invention is carried out at room temperature, and the substrate can also be properly heated for special circumstances. The film-making equipment is a PBAIP-4 ion coating machine or similar equipment.

Large-area thin films can be produced by rotating the substrate holder and mounting multiple cathode targets on the vacuum chamber arms.

Another scheme of the present invention is: provide a kind of transparent MgO thin film prepared according to the method of the present invention, wherein, the thickness of MgO thin film is between 150-2000nm, secondary electron emission coefficient γ is approximately between 0.3～1.5, The optical transmittance is above 80%, such as between 80% and 93%. The atomic content ratio of Mg and O in the thin film is 0.92-1.2, and the atomic content ratio can be selected to be close to 1 specifically.

The transparent MgO thin film prepared by the method of the present invention is not limited to plasma display devices, and can be applied to other fields, such as a stable barrier layer for high-temperature superconducting thin films and ferroelectric thin films.

The beneficial effect of the present invention is: firstly, adopt arc ion plating to prepare transparent MgO thin film, can make full use of the high ionization rate (>90%) that arc ion plating has and the characteristic of high ion bombardment energy, can deposit thin film at low temperature, Its deposition rate is fast, the efficiency is high, and the prepared film is relatively dense; secondly, after combining the pulse bias technology, it has the advantages of high instantaneous energy density and low average energy density, which can not only improve the energy utilization rate, but also reduce the coating process. The temperature of the medium substrate can reduce the interfacial stress caused by the difference in thermal expansion coefficient between the film and the substrate, making the film layer and the substrate more firmly bonded; in addition, the energy of the ions incident on the substrate is adjusted by using negative bias technology, so that To achieve the purpose of controlling the crystallographic orientation of the film, and the chemical composition of the film can also be adjusted by adjusting the partial pressure of the reaction gas and the magnitude of the arc discharge current; Arc ion plating, the prepared MgO film has a dense film layer, a firm bond with the substrate, a high secondary electron emission coefficient, and a long service life. The Mg is fully oxidized by using a working pressure of 1 Pa. Therefore, the Mg in the MgO film The content of impurities is low, thereby effectively improving the transparency of the MgO film; moreover, when using magnetic filtration, it can effectively eliminate large particles and neutral particles in the cathodic arc plasma, and almost 100% pure ions can be obtained, The prepared film is smoother, harder, denser and more uniform; finally, after the vacuum chamber is evacuated in the method of the present invention, the substrate does not need to be heated, and when the substrate is cleaned by glow discharge, _H2 gas does not need to be introduced. These features reduce the cost and complexity of the process. At the same time, the substrate does not need to be cleaned with HF acid in the method of the present invention, thereby avoiding the influence on the transparency of the substrate, and the process is simple, without using toxic, harmful and dangerous gases , no pollution.

The present invention will be further described below in conjunction with the examples, but the present invention is not limited to these examples, and any improvement or substitution on the basic spirit of the present invention still belongs to the scope of protection claimed in the claims of the present invention.

Detailed ways

Example 1

As one of the specific implementations of the present invention, at room temperature, the cathodic arc ion plating method is adopted, the equipment is a PBAIP-4 type ion coating machine, pure magnesium is used as the cathode target, the anode is connected to the vacuum chamber, and the cathode and the anode are respectively connected to the Negative and positive poles of low-voltage, high-current DC power supply; glass slides, silicon wafers or stainless steel sheets are used as substrates, ultrasonically cleaned with ethanol for 10 minutes, then dried, and fixed on the substrate holder in the vacuum chamber facing the target surface. The vacuum chamber was evacuated to 6×10 ^-3 Pa, Ar gas was introduced to 2.0 Pa, a square waveform pulse bias voltage -1100V was applied to the substrate, and the duty ratio was adjusted to 5%, and the plasma generated by Ar gas glow discharge was used to The surface of the substrate is bombarded and cleaned for 10 minutes; after the bombardment is stopped, the reaction gas O ₂ is introduced at a flow rate of 200 SCCM, and Ar gas is used as a protective gas, and the flow ratio of Ar/O ₂ is about 1/20. A square waveform pulse bias of -150V was applied to the substrate with a duty ratio of 5%. The arc was ignited by the contact short circuit method. The arc current was 50A, the working pressure was 1.0Pa, and the deposition time was 7 minutes. A MgO film with dense and uniform film layer, visible light (380-900nm) transmittance higher than 93%, and MgO(200) preferred orientation is prepared. The thickness of the film is 1230nm, and the atomic content ratio of Mg and O in the film is Mg The value of /O is 0.96.

Example 2

As one of the specific implementations of the present invention, at room temperature, the cathodic arc ion plating method is adopted, the equipment is a PBAIP-4 type ion coating machine, pure magnesium is used as the cathode target, the anode is connected to the vacuum chamber, and the cathode and the anode are respectively connected to the Negative and positive poles of low-voltage, high-current DC power supply; glass slides, silicon wafers or stainless steel sheets are used as substrates, ultrasonically cleaned with ethanol for 10 minutes, then dried, and fixed on the substrate holder in the vacuum chamber facing the target surface. The vacuum chamber was evacuated to 5.6×10 ^-3 Pa, Ar gas was introduced to 2.0 Pa, a square waveform pulse bias voltage -1100V was applied to the substrate, and the duty ratio was adjusted to 5%, and the plasma generated by Ar gas glow discharge was used to The surface of the substrate was bombarded and cleaned for 10 minutes; after the bombardment was stopped, the reaction gas O ₂ was introduced at a flow rate of 200 SCCM, and Ar gas was used as a protective gas, and the flow ratio of Ar/O ₂ was about 1/20. Apply a square waveform pulse bias of -750V to the substrate, with a duty ratio of 5%, ignite the arc by contact short circuit method, the arc current is 50A, the working pressure is 1.0Pa, and the deposition time is 7 minutes. A MgO film with a dense and uniform film layer, a visible light (380-900nm) transmittance higher than 93%, and a mixed orientation of MgO (200) and (220) is prepared. The thickness of the film is 1030nm, and the atoms of Mg and O in the film The value of the content ratio Mg/O was 1.0.

Example 3

As one of the specific implementations of the present invention, at room temperature, the cathodic arc ion plating method is adopted, the equipment is a PBAIP-4 type ion coating machine, pure magnesium is used as the cathode target, the anode is connected to the vacuum chamber, and the cathode and the anode are respectively connected to the Negative and positive poles of low-voltage, high-current DC power supply; glass slides, silicon wafers or stainless steel sheets are used as substrates, ultrasonically cleaned with ethanol for 10 minutes, then dried, and fixed on the substrate holder in the vacuum chamber facing the target surface. The vacuum chamber was evacuated to 4×10 ^-3 Pa, Ar gas was introduced to 1.5 Pa, a square waveform pulse bias of -900V was applied to the substrate, and the duty ratio was adjusted to 5%, and the plasma generated by Ar gas glow discharge was used to The surface of the substrate is bombarded and cleaned for 10 minutes; after the bombardment is stopped, the reaction gas O ₂ is introduced at a flow rate of 210 SCCM, and Ar gas is used as a protective gas, and the flow ratio of Ar/O ₂ is about 1/20. There is no substrate bias, the arc is ignited by the contact short circuit method, the arc current is 70A, the working pressure is 1.2Pa, and the deposition time is 10 minutes. A MgO thin film with dense and uniform film layer, visible light (380-900nm) transmittance higher than 90%, and (220) preferred orientation is prepared. The thickness of the film is 977nm. The value of O is 1.1.

Example 4

As one of the specific implementations of the present invention, at room temperature, the magnetic filter cathodic arc ion plating method is adopted, the equipment is a PBAIP-4 ion coating machine, the magnetic filter device is a 1/4 elbow, and a cathode target is installed at one end of the elbow , and the other end is connected to the vacuum chamber as an ion outlet. Use pure magnesium as the cathode target, connect the anode to the vacuum chamber, and connect the cathode and anode to the negative and positive electrodes of a low-voltage, high-current DC power supply respectively; use glass slides, silicon wafers or stainless steel sheets as substrates, and use ethanol to ultrasonically clean them for 10 minutes After blowing dry, the ion outlet is fixed on the substrate holder in the vacuum chamber, and the substrate holder is connected to the negative electrode of the bias power supply. The vacuum chamber was evacuated to 5.3×10 ^-3 Pa, and Ar gas was introduced to 3.0 Pa, and a square waveform pulse bias of -900V was applied to the substrate with a duty ratio of 5%. The bottom surface was bombarded and cleaned for 10 minutes; after the bombardment was stopped, the reaction gas O ₂ was introduced with a flow rate of 30 SCCM, Ar gas was used as the protective gas, and the pulse bias voltage applied to the substrate was -150V, and the duty cycle was 5%, magnetic filter coil current 7.5A. The arc is ignited by the contact short circuit method, the arc current is 30A, and the arc voltage is 40V. The working pressure is 0.2Pa, and the deposition time is 20 minutes. A MgO thin film with dense, uniform, good adhesion and MgO(220) preferred orientation is prepared. The thickness of the thin film is 240nm. The size of the large particles on the surface of the film is less than 600nm. The secondary electron emission coefficient at a beam energy of 400 eV was 1.18.

In the present invention, during film coating, the partial pressure of the protective gas Ar is generally lower than the partial pressure of the reaction gas O ₂ . In our experiments, the ratio of the two is generally kept at 1/20, and the protective gas is often used as Ar gas, which is easy to ionize and beneficial to arc ignition, and is chemically inert. At present, there is no use of other inert gases as shielding gases in literature reports, nor have they been used in our experiments.

Claims (8)

1. method that adopts the arc ion plating method to prepare transparent MgO film, this method comprises:

Make the negative electrode target with pure magnesium;

Substrate is placed in the vacuum chamber;

Feed Ar gas to described vacuum chamber, and utilize the glow discharge of Ar gas under the high bias voltage that described substrate surface is bombarded cleaning;

Described bombardment feeds reactant gases O to described vacuum chamber after cleaning and finishing ₂With shielding gas Ar, making the operating pressure in the vacuum chamber is 0.2～4Pa;

Apply the negative bias of 0～1000V to described substrate; And

The electric arc that ignites begins plated film.

2. the method for claim 1, it is characterized in that: described negative bias is a pulsed bias, dutycycle is 3%～20%.

3. method as claimed in claim 1 or 2 is characterized in that: the described reactant gases O that feeds in described vacuum chamber ₂Flow be 50～260sccm, the operating air pressure during plated film in the described vacuum chamber is 0.2～4Pa, flame current is 45～100A.

4. method as claimed in claim 1 or 2 is characterized in that: further adopt magnetic filter, described negative electrode target is installed in an end of described magnetic filter, and the other end of described magnetic filter links to each other with described vacuum chamber as ion outlet.

5. method as claimed in claim 4 is characterized in that: the described reactant gases O that feeds in described vacuum chamber ₂Flow be 5～100sccm, the operating air pressure during plated film in the described vacuum chamber is 0.2～0.8Pa, flame current is 15～80A.

6. the method for claim 1 is characterized in that: before described bombardment is cleaned, described substrate also is fixed in after the drying more than 3 minutes on the substrate holder in the described vacuum chamber with the ethanol ultrasonic cleaning, described vacuum chamber is evacuated to 1 * 10 ^-3～6 * 10 ^-3Pa feeds Ar gas to 0.5～3.5Pa, and the described high bias voltage that applies is the pulsed bias of 400～1100V, dutycycle 3%～20%, and the time that described bombardment is cleaned is 5～20 minutes.

7. the method for claim 1, it is characterized in that: described substrate comprises slide glass, silicon chip or stainless steel substrates, and described negative electrode target adopts highly purified magnesium, and the depositing time during plated film is 5～30 minutes.

8. transparent MgO film according to the preparation of the described method of one of claim 1～7, it is characterized in that: the thickness of described MgO film is between 150～2000nm, (Ne ion-accelerating voltage 250～400V) between secondary electron yield γ is roughly 0.3～1.5, optical transmittance is more than 80%, and the ratio of the atom content of Mg and O is 0.92～1.2 in the film.