Pulsed Laser Deposition and Thermal Evaporator System – PLD-T

Substrate Heater: To heat the substrate for growing crystalline films.A PLD system typically contains four key components, including:

• Laser: Typically an excimer (KrF, ArF) or Nd:YAG laser.

• Vacuum Chamber: Contains the target and substrate to have a clean deposition.

• • • Target: The material to be laser-ablated and deposited. 

• The greatest advantage of utilizing PLD technique for thin film deposition is stoichiometric transfer of the target material onto the substrate, which means the film's chemical composition is very close to the target's composition. This is crucial for complex materials like high-temperature superconductors (YBa₂Cu₃O₇) and complex oxides.

• PLD method is widely used in coating various thin films of different materials, such as:

  • High-Temperature Superconductors 
  • Complex Oxides (ferroelectrics, multiferroics, piezoelectrics)
  • Dielectrics (SiO₂, HfO₂)
  • Nitrides (TiN, GaN)
  • Diamond-Like Carbon (DLC) films
  • Metals and Semiconductors
  • Biomaterials (e.g., hydroxyapatite)

• PLD generally has better stoichiometric transfer for complex oxides compared to sputtering deposition, while sputtering technique benefits in providing thickness uniformity of thin film deposition over larger specimen, and is more established in industry.

  MBE technique provides the ultimate control at an atomic level and superior film quality but is much slower, more complex, and far more expensive than PLD. 

  In general, the PLD technique advantages include:

  • Stoichiometric Transfer: Excellent for multi-component materials.
  • High Deposition Rate: Relatively fast compared to some other techniques.
  • Versatility: Can deposit virtually any material—metals, semiconductors, insulators, polymers—simply by changing the target and using the proper laser.
  • Clean Process: The laser is outside the chamber, minimizing contamination.
  • Reactive Deposition: Easily done by adding a background gas (e.g., O₂, N₂).

• Droplet Formation: Molten droplets or solid particulates can be ejected from the target and land on the film, creating defects.
• Small Deposition Area: The plasma plume is highly directional, leading to non-uniform thickness over large areas. This makes it less suitable for industrial coating of large wafers.
• Cost: High-power pulsed lasers are expensive to purchase and maintain.
• Film Thickness Uniformity: Requires careful optimization of the target-to-substrate distance and plume dynamics.

• The droplets or particulates generated during the pulsed laser deposition from the target, are caused by subsurface boiling, splashing of molten material, or exfoliation of fragile target material.

  The solutions to this problem include:

  • Optimizing laser fluence (not too high)
  • Using a smooth, polished target
  • Rotating the target
  • Using off-axis PLD (placing the substrate outside the direct line of sight of the target)
  • Using a mechanical velocity filter to block droplets

• On-Axis: The substrate is placed directly in front of the target plume, giving high growth rates but susceptible to droplet deposition.
• Off-Axis: The substrate is placed facing parallel to the target surface, so the film grows at a lower deposition rate from material that scatters in the gas phase, effectively filtering out droplets, resulting in much smoother films.

• The higher the ultimate chamber vacuum (base pressure), the more contaminant gases (like O₂, H₂O, N₂) are removed. So the plasma plume can travel to the substrate in a high vacuum chamber without reacting or scattering, leading to a pure film.

• For depositing oxide materials, a background/process oxygen pressure helps to provide the oxygen needed during the deposition process to insure the correct thin film structure and properties and the proper film stoichiometry. 

• Heating the substrate provides thermal energy the arriving atoms to move on the surface or diffuse in the coated film and place in the correct crystal lattice sites, hence forming a high-quality, crystalline film instead of a disordered, amorphous one.

• The most important PLD parameters include:

  • Laser Fluence: Laser energy per unit area on the target. It must be above the "ablation threshold" to create a plasma.
  • Substrate Temperature: Critical for the crystallinity of the film.
  • Background/process Gas Pressure: Determines the composition, phase, and even the stress of the film.

• Target rotation ensures uniform erosion of the target surface and prevents drilling a single deep pit into the target, which would change the ablation characteristics and create non-uniform particles.

• It depends on the customer. Some customers already have a laser or have good quality laser manufacturers in their country and we prefer to buy the laser themselves due to reduced shipping costs and better after-sales service, but if they are willing, we will buy the laser for them.

• According to the target material, substrate properties, the resulting layer compound etc., there are several features that should be determined prior to employing a laser for a PLD process, including pulse energy and duration, and laser wavelength.

• The laser features strongly depends on the desired application. The 1064 nm wavelength Nd-YAG laser that are mostly used in coating systems are offered in a wide range of single pulse energies and durations, rising the necessity to determine the required energy to be transferred to the target material type to be ablated. Excimer lasers are preferred for materials requiring high photon energy for ablation, such as coating DLC layers, RF-piezo, while femtosecond lasers are ideal for applications needing high precision and minimal thermal effects.

• No, the laser is controlled completely independent of the vacuum chamber and the coating system. 

• The laser and PLD machine can be placed on one table or two separate tables. The height of the table on which the laser or machine is placed should be such that the laser beam can pass through the PLD viewport and hit the target.

• Most lasers require a chiller, and when purchasing a laser, a suitable chiller must be purchased. However, if the device the customer wants is a PLD-T model, which in addition to PLD also has thermal evaporation capabilities, a chiller is required to cool its high-current electric feedthroughs and the thickness gauge crystal holder. For example, the S&A model CW3000 chiller is a chiller that can be used for both lasers and thermal evaporation feedthroughs at the same time.

• Two, one water-cooled, which is used when we use the thermal evaporation section of the device and its location is fixed, and one that is mobile and not water-cooled, that is used for the PLD process.

• The standard target diameter is 20 millimeters, but it can be customized due to customer’s need.

• It depends on the wavelength of the laser beam and must be chosen in such a way that it does not absorb the laser light, for example, if using an excimer laser with a wavelength of about 248 nm, fused silica (quartz) viewport provides better transmission in the UV range.  

• Working with lasers in a PLD process requires carrying out safety precautions, before and during the coating process, to prevent life-threatening laser hazards. Some of the safety recommendations are listed below:

  • Use appropriate laser safety glasses.
  • Never stare at the beam.
  • Remove reflective objects, like jewelry, from the beam path (also, anti-reflective coatings on the viewports can be used).
  • Use proper warning signs in the area laser is operating.
  • All laser equipment should be grounded to prevent electrical hazards.
  • Manage the system cables to avoid having excessive wires or cables on the floor.
  • Work with qualified personnel.