Thin Film Deposition

Pulsed Laser Deposition (PLD)

Pulsed laser deposition (also known as Laser-MBE) is used for growing thin films from stoichiometric targets out of thermal equilibrium. A pulsed ultraviolet laser beam produces a stoichiometric plasma plume out of the polycrystalline target material. The substrate sits within this plasma plume so that a thin film of the plasma material is being deposited onto the substrate. Because of their high melting points, PLD is especially suited for growing thin oxide films.

In our system, the substrate is heated from the back by an infrared heating laser at a wavelength of 938 nm with a maximum power of 140 W located outside the deposition chamber. The temperature is also measured from outside the chamber using a two-color pyrometer. On silicon substrates, we achieve a maximum temperature of 1300°C. At the bottom there are five polycrystalline PLD targets mounted on a target carousel. An ultraviolet laser beam from a KrF excimer laser (Lambda Physik COMPex 201) of 248 nm with a pulse energy of 680 mJ and a repetition rate of 10 Hz is focused by a telescope objective onto the target surface. An in-situ RHEED system is used to monitor the growth process.

Advantages:

• stoichiometric transfer of material
• high deposition rates
• high flexibility and variety of materials

Our PLD system is used for growing ferromagnetic, ferroelectric, semiconducting, and insulating oxides, like Sr₂CrReO₆, BiCrO₃, BaTiO₃, SrTiO₃, Fe₃O₄, Y₃Fe₅O₁₂, and ZnO.

Movie of the pulsed laser deposition process (avi, 10M)

Electron Beam Evaporation

Thermal evaporation is one of the oldest thin film deposition methods. In a vacuum chamber, the source material is heated above its melting point. This may be done by resistive heating for materials with low melting points or by electron beam heating. The material is then evaporated and deposited on a substrate located above the heated source.

Our electron-beam evaporation system contains four crucibles for four different source materials. The electron beam comes from the bottom and is directed by a magnetic field to the surface of the source materials. The beam heats the material above its melting point. The maximum temperature is about 2000°C. The material is evaporated and deposited on the surface of the substrate. The substrates may be cooled using liquid nitrogen. The film thickness can be monitored in-situ by an oscillating quartz crystal.

Electron beam evaporation has the advantage of being highly directional thus enabling shadow evaporation. We use electron-beam evaporation for depositing thin films of Co, Ni, Au, Al, and SiO_x.

Sputtering

Sputtering is very common for a broad range of materials. Like PLD, it is a non-thermal process based on a momentum transfer from accelerated energetic particles with energies between eV and keV to the atoms of the target material. These "sputtered" atoms are then deposited on the substrate surface.

Sputtering allows to deposit a broad range of materials with high reproducibility and scalability.

Our sputtering chamber is equipped with three sputtering guns (Nb, NiPd, Al) and an Ar ion beam gun for surface cleaning. The sputtering chamber is attached to the central transfer chamber of the UHV cluster tool. In this way it is possible to combine sputtering of metallic multilayers with various other options provided by the UHV cluster tool such as electron beam evaporation, pulsed laser deposition, or in-situ surface characterization by AFM/STM.

Metal MBE

A new UHV metal-MBE systems has benn recently set up at the WMI. The system has a sample holder, which can be rotated and tilt and therefore allows large flexibility for shadow evaporation processes used. The system is presently equipped with a an electron beam evaporation system with 6 crucibles for 6 different materials. The system can be eventually be upgraded with up to 6 effusion cells. The sample holder can be cooled by liquid nitrogen.