Stress-free ALD from Picosun
Picosun Group, a supplier of Atomic Layer Deposition (ALD) thin film coating solutions, has reported a new method to control and eliminate stress in ALD films.
Various stresses are easily formed in ALD films during the deposition process, either inside the film or between the film and the underlying substrate. As all modern microelectronic devices are basically built by stacking ultra-thin layers of various materials on top of each other, these stresses can be detrimental not only to the film itself but to the other functional layers and structures beneath.
In devices (such as MEMS) where cavities and free-standing membranes are often employed, stress-free ALD films, or films where the stress is exactly controlled, are very much sought after. The same applies for IC components, where film strains and tensions can lead to material layers detaching from each other, or bending and buckling of the whole structure.
Picosun has now developed a method with which zero stress and controlled stress ALD films can be produced. This sophisticated method is based on intricate tuning of process chemistry and deposition conditions. The desired effect is obtained with right selection of precursor chemicals and process temperature, so no additional process steps such as heat or plasma treatments (which might cause structural damage to the film) are required. Replacing a single material film with carefully designed nanolaminate of materials with opposite stress properties is another way to achieve zero stress layers. These methods have been validated with e.g. HfO2, which is one of the key materials in microelectronics industry.
Other ALD materials tested include SiO2, Ta2O5, and TiO2. (These were done in collaboration with VTT Technical Research Centre of Finland. Stress measurements were performed at VTT. The results were initially published in the AVS 18th International Conference on Atomic Layer Deposition (ALD 2018), Incheon, South Korea)
