Working Mechanism of Pulsed Laser Deposition

Pulsed laser deposition (PLD) is a physical vapor deposition (PVD) technique where a high-power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited.  Although the equipment of pulsed laser deposition (PLD) system is simple, its working mechanism is related to many complicated physical phenomena. It includes all physical interactions between the laser and the substance when the high-energy pulsed radiation strikes the solid sputtering target, the formation of plasma plumes and the transfer of the molten material through the plasma plume to the surface of the heated substrate. Therefore, PLD can generally be divided into the following three stages:

Interaction between laser radiation and the sputtering target

In this stage, the laser beam is focused on the surface of the target materials. When sufficient high energy flux and short pulse width are achieved, all elements of the target surface are rapidly heated to the evaporation temperature. At this point, the material in the target will be sputtered from the target. The instantaneous melting rate of the target is highly dependent on the flow of laser light onto the target. The melting mechanism involves many complex physical phenomena such as collisions, heat, excitation with electrons, delamination, and fluid mechanics.

Dynamics of molten matter

In the second stage, according to the law of aerodynamics, the sputtered particles have a tendency to move toward the substrate. The space thickness varies with the function cosn θ, and n>>1. The area of the laser spot and the temperature of the plasma have an important influence on the uniformity of the deposited film. The distance between the target and the substrate is another factor that affects the angular extent of the molten material. It has also been found that placing a baffle close to the substrate narrows the angular extent.

Deposition of molten material on the substrate

The third stage is the key to determining the quality of the film. The high-energy nuclides emitted hit the surface of the substrate and may cause various damages to the substrate. The high energy nuclide sputters some of the atoms on the surface, and a collision zone is established between the incident stream and the sputtered atoms. The film is formed immediately after the formation of this thermal energy zone (collision zone), which is the best place to condense particles. As long as the condensation rate is higher than the release rate of the sputtered particles, the heat balance condition can be quickly reached, and the film can be formed on the surface of the substrate due to the weakened flow of the molten particles.

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Advantages and Disadvantages of Pulsed Laser Deposition (PLD)

Pulsed laser deposition is one of the methods of thin film preparation, and several others include chemical vapor deposition, material sputtering, and etc. Pulsed Laser Deposition (PLD), also known as Pulsed Laser Ablation (PLA), uses a laser to bombard the surface of the target, raising its surface temperature and further producing high temperature and high pressure plasma ( T>104K), depositing on different substrates to form a film.

Advantages

1 It is easy to obtain multi- component film that is of the desired stoichiometric ratio by PLD.

2 It has high deposition rate, short test period and low substrate temperature requirements. Films prepared by PLD are uniform.

3 The process is simple and flexible with great development potential and great compatibility.

4 Process parameters can be arbitrarily adjusted, and there is no limit to the type of PLD targets. Multi-target components are flexible, and it is easy to prepare multilayer films and heterojunctions.

5 It is easy to clean and can prepare a variety of thin film materials.

6 PLD uses UV pulsed laser of high photon capability and high energy density as the energy source for plasma generation, so it is non-polluting and easy to control.

 Pulsed laser deposition

Disadvantages

1 For quite a number of materials, there are molten small particles or target fragments in the deposited film, which are sputtered during the laser-induced explosion. The presence of these particles greatly reduces the quality of the film.

2 The feasibility of laser method for large area deposition has not been proved yet.

3 Average deposition rate of PLD is slow.

4 In view of the cost and deposition scale of laser film preparation equipment, it seems that PLD is only suitable for the development of high-tech fields such as microelectronics, sensor technology, optical technology and new material films.

 

Stanford Advanced Materials (SAM) Corporation is a global supplier of various sputtering targets such as metals, alloys, oxides, ceramic materials. Please visit our website https://www.sputtertargets.net for more information.