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Thin film deposition technologies are of paramount importance in today’s fast growing industrial world of microelectronics, optics and space technologies. They allow the physical, chemical, electric, magnetic, mechanical properties, and surface morphology of materials to be modified without altering the composition and microstructure of the bulk material. A 2–dimensional layer of any material, with thicknesses ranging from a few atomic layers to microns, are qualified as thin films. Most often, thin films are deposited in plasma environment.
The uniqueness of plasma assisted deposition processes lies in their ability to synthesize complex films at relatively low substrate temperatures. These processes enable film properties to be varied over a wide range by controlling the plasma conditions and the plasma’s interaction with the material surface. For example, by source varying power, the ion density and electron temperature can be changed, which impacts the deposition rate and the balance of chemistry in the deposition environment. Broadly, plasma assisted thin film deposition techniques can be categorized in three groups, namely, Sputtering, Plasma Enhanced Chemical Vapor Deposition (PECVD) and Atomic Layer Deposition (ALD).
Sputtering is a vital and prominent process for thin film depositions. In this process, a substrate to be coated is placed in a vacuum chamber containing an inert gas – usually Argon – and a negative bias is applied to the target causing the plasma to form in the vacuum chamber. So, the target is attached to the cathode and substrate to the anode. Ions from the plasma are accelerated towards cathode (target) where they hit the target with sufficient energy to dislodge some atoms/molecules. These sputtered materials from the target travel across the chamber and are deposited on the substrate surface. By changing the ionization rate (or ion/neutral ratio), the resulting film properties can be tailored.
Find out more about Sputtering here.
In the Chemical Vapor Deposition (CVD) method, the gas phase constituents react with the substrate surface, causing the material to be deposited. The process is limited by the substrate temperature, which is the only source of energy to promote surface chemistry. Plasma Enhanced Chemical Vapor Deposition (PECVD) offers enhanced deposition rates at reduced substrate temperature since the reactants are in the form of plasma. The electron temperatures in the plasma drive the chemistry, instead of the neutral gas temperature. This enables the treatment of materials like plastic or fabric, which otherwise wouldn’t survive the CVD temperatures.
Find out more about PECVD here.
Atomic Layer Deposition (ALD) or Pulsed-Enhanced Atomic Layer Deposition (PEALD) is the most advanced material processing technique, which enables the deposition of highly conformal films on semiconductor wafers. This technology provides accurate thickness control and robust film properties, and this is extremely beneficial when it comes to semiconductor applications.
Find out more about ALD here.
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