Pulsed laser deposition is a method of focusing the laser on a small area on the target material, using the high energy density of the laser to evaporate or even ionize part of the target material, so that it can separate from the target material and move toward the substrate, and then deposit on the substrate to form a thin film. 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, and even to prepare some difficult-to-synthesize material films, such as diamond and cubic nitride films.
Pulsed Laser Deposition System (PLD)
TSST pulsed laser deposition system configuration:
Growth chamber, injection chamber optional
Two target platforms available
Three types of heaters are available, with the highest heating temperature of 1200℃
High pressure RHEED, working pressure can reach 100Pa
Flanges can be reserved for LEED, K-Cell, etc.
Optional: ozone generator, ion source, mask system, etc.
The PLD system equipment is simple, but its principle is very complicated. Physical phenomenon It involves high energy When the pulsed radiation impacts the solid target, all the physical interactions between the laser and the material also include the formation of the plasma plume, the subsequent transfer of the melted material through the plasma plume to the heated substrate surface, and the final film formation process. Therefore, PLD can generally be divided into the following four stages:
4. Nucleation and growth of thin films on substrate surfaces
In the first stage, the laser beam is focused on the surface of the target. When a sufficiently high energy flux and short pulse width are achieved, all elements on the target surface are rapidly heated to the evaporation temperature. The material separates from the target, and the composition of the evaporated material is the same as the stoichiometry of the target. The instantaneous melting rate of the material depends greatly on the flux of the laser irradiated on the target. The melting mechanism involves many complex physical phenomena, such as collision, heat, excitation of electrons, delamination, and fluid mechanics.
In the second stage, according to the laws of gas dynamics, the emitted material tends to move toward the substrate and a forward scattering peak occurs. The spatial thickness varies as a function of cosnθ, with n>>1. The area of the laser spot and the temperature of the plasma have an important influence on whether the deposited film is uniform. The distance between the target and the substrate is another factor that governs the angular range of the melted material. It has also been found that placing a baffle close to the substrate reduces the angular range.
The third stage is the key to determine the quality of the film. The emitted high-energy nuclides hit the substrate surface and may cause various damages to the substrate. The following figure shows the mechanism of interaction. The high-energy nuclides sputter some atoms on the surface, and a collision zone is established between the incident flow and the sputtered atoms. The film is formed immediately after the formation of this thermal energy zone (collision zone), which happens to be the best place for condensation particles. As long as the condensation rate is higher than the release rate of the sputtered particles, the thermal equilibrium state can be quickly reached, and the film can be formed on the substrate surface due to the weakening of the molten particle flow. [1]
Key Advantages of PLD
1. It is easy to obtain multi-component films with desired stoichiometric ratios, i.e., they have good composition retention;
2. High deposition rate, short test cycle, low substrate temperature requirement, and uniform film preparation;
3. The process parameters can be adjusted arbitrarily, and there is no restriction on the type of target material;
4. Huge development potential and great compatibility;
5. Easy to clean and process, and can be used to prepare a variety of film materials.
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