Atomic layer deposition

ALD

  • Cyclic CVD process 
  • Precise thickness control on highly conformal layers
  • Proper for semiconductor electronics and optics

Conformal films on any shape

Atomic layer by atomic layer - cyclically until the desired film is achieved

Atomic layer deposition (ALD) is used for deposition of thin coatings where coating deposition on the surface and layer thickness precision is of great priority. ALD is a type of CVD process in which the layer formation is produced through two or more cyclically alternating surface reactions.

The main application of ALD was and still is in semiconductor electronics, such as the formation of high-k gate insulators in MOSFETs. However, other industries are increasingly taking advantage of ALD technology as well; such as in the production of MEMS, barrier coatings, optical or functional coatings on particles or in capillaries.

In contrast to conventional CVD processes, where the precursors react continuously and at least partially in the gas phase, in the ALD process this takes place exclusively on surfaces, e.g. the substrate surface. It is a cyclic process that consists of multiple partial reactions. For this, the substrate is brought into contact with the precursors in an alternating manner - never simultaneously. Only a partial reaction takes place at any given time on the substrate surface. The individual reaction steps are self-limiting meaning the chemical compounds of this surface are the only compounds available to the precursor for layer growth. If there are no free reaction species any longer, then the partial reaction is completed. The process chamber is evacuated and/or purged with inert gas between the individual reaction steps. This removes any cross contamination from the previous precursor molecules.

A single atomic layer is deposited in each cycle. Coating usually takes place in a reactor chamber and the gases are supplied successively. Alternatively, it is also possible to transport the substrate between two zones filled with different precursors (spatial ALD). The entire process sequence including all reactions and purging activities is repeated several times to achieve the desired layer thickness. After a certain initial phase that is a result of the surface properties, the coating thickness increases proportionally to the number of reaction cycles; this allows for very precise control of the layer thickness.

ALD can also be used for depositing ultra-thin functional layers with excellent thickness uniformity even on surfaces with challenging shapes. The process temperature for this method is relatively low, usually ranging from 150 °C to 400 °C. Plasma or particularly reactive precursors can also be used to reduce the reaction temperatures even further.

FHR designs and manufactures ALD systems tailor-made to the customer's requirements and wishes. FHR's ALD tools’ features are easily configurable with regards to the chamber layout, gas supply, bubbler system and heating and cooling options. We can offer platforms with 100, 150 and 300 mm in diameter, as well as ALD modules for integration into cluster tools. Custom-made tools based on ALD technology are also an option. 

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Contact Atomic Layer Deposition

Dr. Hannes Klumbies
Product Management

+49 35205 520-292 hannes.klumbies[at]fhr.de