Ion Beam Sputtering (IBS) Technology

Ion Beam Sputtering

Ion beam sputtering (IBS), also known as ion beam deposition (IBD), is a thin film deposition technique to produce high-quality thin films of various materials ranging from metals to semiconductors and dielectrics. This deposition technique is widely used in the optics industry, where dense, uniform layers are essential. IBS offers the advantage of replicability, low impurity level of thin films along with strict control over the layer stoichiometry compared to thin films made by conventional magnetron sputtering (MS). In an IBS process, a broad beam of collimated ions strikes the target; as a result, target atoms (or molecules) are sputtered and then relax on the substrate.

Mechanism

In a typical sputtering process, once the energetic inert gas (Argon or Xenon) ions hit the target, the atoms (or even molecules) of the target are knocked out. These ejected particles have high kinetic energy in the range of 1-10 eV and therefore form very compact, pinhole-free thin layer. A schematic of the sputtering process is displayed in Figure 1.

There are a number of key components inside an Ion Beam Sputtering Deposition chamber: 1. Ion source, 2. Target, and 3. Substrate holder as shown in Figure 2. Inside the ion source, a high voltage of 2-10 kV is applied between the cathode and the anode with common central axis, which ionizes Argon (Ar) atoms. Positively charged Ar ions accelerate toward the grid or filament in the throat of ion source and leave it on their way towards the target.

The ion source produces highly energetic beam and therefore generates films with excellent adhesion and high packing density. Typical pressure during IBS process is about 10^-4 Torr, which is lower than the nominal pressure of the conventional sputtering process. This is a result of delimiting Ar plasma inside the ion source, allowing lower pressures in the chamber, which is beneficial in lower impurity rate of the deposited film.

• There are two other method of utilizing ion beam sputtering for thin film deposition:

Ion Beam Assisted Deposition (IBAD)

In some cases, a secondary ion source is also utilized either to clean the substrate before the deposition or to perform ion beam assist deposition (IBAD). IBAD is of interest especially where metal oxide or nitride films are to be deposited since it improves the density, optical properties and moisture stability of the film. In IBAD the second ion source is referred to as Assist Ion Source.

Reactive Ion Beam Deposition (RIBD)

To perform reactive ion beam deposition (RIBD), a non-inert gas (i.e. O₂ or N₂) is introduced to the chamber, which reacts with the sputtered atoms to form oxide or nitride compound on the substrate.

The multi-target configuration enables the deposition of alloys or compounds from multiple targets in a single process. Rotating substrates during deposition enhances film uniformity. To improve the film quality further, rotary planetary substrate holders are favorable over single-rotation specimen stages.

Advantages of Ion Sputtering

Ion Sputtering is widely known to produce highest quality films in terms of performance and precision. This deposition method is used wherever film thickness, stoichiometry and uniformity are to be controlled strictly. Ion beam sputtering can produce smooth and dense thin films with thicknesses ranging from angstrom-scale to micrometers, excellent for precision optics. A major advantage of IBS over other sputtering methods is the control over several different parameters including ion energy, angle of incidence, and target sputtering rate almost independently. This enables enhanced process stability and stable deposition rates. Another important strength of IBSD is the possibility of coating different material classes from metals to insulators.

Drawbacks

Low deposition rate and high cost are considered as IBD disadvantages compared to other physical vapor deposition (PVD) methods.

Applications of IBD

Because of the numerous merits of IBD, including extremely uniform and very dense coatings, strong adhesion of thin film to the substrate, low-temperature and low-loss process, high damage threshold, and low-stress film forming, it is ideal for precision optics or semiconductor production. There are a wide range of IBD applications from deposition of high corrosion resistant films, optically smooth surfaces e.g. anti and high reflective filters, beam splitters, extreme UV (EUV) mirrors, laser facets, flat and smooth interfaces for multi-layer depositions as in metal oxide, and transparent conductive oxides (TCO) depositions in the OLED and flexible display industry.

Vac Coat Sputter Coaters

Vac Coat offers vacuum deposition systems using different coating methods, such as thermal evaporation, sputtering and pulsed laser deposition. Desktop low/high vacuum sputtering and carbon coating systems DSCR/DSCT are two ideal SEM Coaters for electron microscopy sample preparation, whereas more advanced triple target sputtering systems and thermal evaporation with angled/straight cathodes (DST3-TA/S) fulfill nearly all research demands.

Our new sputtering system with thermal evaporation designed for glove box DST2-TG, has the full advantage of fast switching between the two deposition methods without breaking the vacuum.

References

1. https://polygonphysics.com/applications/ion-beam-sputter-deposition
2. Bundesmann, Carsten, and Horst Neumann. “Tutorial: The systematics of ion beam sputtering for deposition of thin films with tailored properties.” Journal of Applied Physics 124.23 (2018): 231102.
3. https://en.wikipedia.org/wiki/Ion_beam_deposition
4. Ohashi, Kenya, Kiyoshi Miyake, and Tetsuroh Minemura. “Formation of high corrosion resistant iron films by ion beam deposition method.” Advanced Materials’ 93. Elsevier, 1994. 207-210.
5. Miyake, K. (2002). Ion-Beam Deposition. In: Waseda, Y., Isshiki, M. (eds) Purification Process and Characterization of Ultra High Purity Metals. Springer Series in Materials Processing. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56255-6_7