Pulsed laser deposition (PLD) is to fPulsed laser deposition (PLD) is to focus the laser on a small area on the sputtering target, and use the high energy density of the laser to evaporate or even ionize part of the target material, so that it can move away from the target and move to the substrate. A method of depositing on a substrate to form a thin film.
Principle of Pulsed Laser Deposition (PLD)
The entire PLD coating process is usually divided into three stages.
1. The laser interacts with the target to generate plasma. The laser beam is focused on the surface of the target. At a sufficiently high energy density and short pulse time, the target absorbs the laser energy and causes the temperature at the spot to rise rapidly above the evaporation temperature of the target, resulting in high temperature and ablation. The target material vaporizes and evaporates, and atoms, molecules, electrons, ions, molecular clusters, micron-scale droplets, solid particles, etc. escape from the surface of the target. These evaporated substances in turn continue to interact with the laser, and the temperature is further increased to form a regionalized high-temperature and high-density plasma. The plasma absorbs light energy through the inverse bremsstrahlung absorption mechanism and is heated to above 104K, forming A bright plasma flame with a dense core.
2. After the plasma flame is formed, it continues to interact with the laser beam and further ionizes. The temperature and pressure of the plasma rise rapidly, and a large temperature and pressure gradient is formed in the normal direction of the target surface, making it outward along the direction Perform isothermal (during laser action) and adiabatic (after laser termination) expansion. At this time, the non-uniform distribution of the charge cloud forms a relatively strong accelerating electric field. Under these extreme conditions, the high-speed expansion process takes place in an instant of tens of nanoseconds, quickly forming an elongated plasma plume outward along the normal direction.
3. The plasma nucleates and grows on the substrate to form a thin film. The high-energy particles in the laser plasma bombard the surface of the substrate, causing it to produce varying degrees of coarse-shooting damage, one of which is atomic sputtering. A thermalized zone is formed between the incident particle stream and the sputtered atoms. Once the aggregation rate of the particles is greater than the sputtering rate of the sputtered atoms, the thermalized zone will dissipate and the particles will grow a thin film on the substrate.
Features of Pulsed Laser Deposition (PLD)
Pulsed laser deposition technology is currently the most promising film forming technology, which is simple and has many advantages.
(1) Fully equivalent coating can be performed on composite materials with complex chemical composition, which is easy to ensure the stability of the stoichiometric ratio after coating. Easily consistent with the target composition is the biggest advantage of PLD, which distinguishes it from other technologies.
(2) Rapid response and fast growth. Usually, a film of about 1μm can be obtained in one hour.
(3) Strong orientation and high film resolution, which can realize micro-area deposition.
(4) A variety of gases can be introduced in situ during the growth process. The introduction of active or inert and mixed gases is of great significance for improving the quality of the film.
(5) It is easy to make multi-layer films and heterogeneous films, especially heterojunctions of multiple oxides, by simply changing the target.
(6) The target is easy to prepare without heating. The high plasma energy is greater than 10eV, and the ion energy is about 1000eV. Such a high energy can reduce the substrate temperature required for the film, and it is easy to grow a structure with consistent orientation in situ at a lower temperature. And epitaxial single crystal film.
(7) The high-vacuum environment has less pollution to the film and can be made into a high-purity film; Yuhui only transports and evaporates in a local area, so there is much less pollution to the sink cavity.
(8) There are many types of films that can be made, and almost all materials can be made with PLD, unless the material is transparent to the laser.
Pulsed laser deposition (PLD) applications
Among the many thin film preparation methods, pulsed laser deposition technology is the most widely used. It can be used to prepare thin films of various materials such as metals, semiconductors, oxides, nitrides, carbides, borides, silicides, sulfides, and fluorides. It is even used to prepare some difficult-to-synthesize material films, such as diamond and cubic nitride films.