Plasma-Enhanced Chemical Vapor Deposition

Plasma-Enhanced Chemical Vapor Deposition (PECVD) is the process of applying a plasma to gas (or vapor) precursors to deposit a film on a surface.

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Typically, a 13.56 MHz radio frequency (RF) generator applies an electric field to multiple gases between two electrodes in a low-pressure vacuum chamber. The RF energy excites the gases, freeing some of the electrons from their atoms or molecules and thereby creating a plasma. The partially ionized gases in the plasma contain ions, electrons, and neutral atoms. The plasma contains energetic and reactive molecules and is highly electrically conductive. The ions in the plasma interact with each other and with the surface, thereby coating it.

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The resultant coating is typically amorphous, cross-linked, conformal, and pinhole-free.

PECVD-applied coatings can be organic or inorganic. In contrast to conventional polymers, organic films deposited by PECVD have shorter repeating units in their structure.

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PECVD is most often used in the semiconductor industry, but Interlayer specializes in coating three-dimensional (3D) parts, which enables us to address medical device and IVD customer needs.

 

PECVD creates the coating material and applies it to the part in a single step. Any necessary pretreatment such as cleaning and activation are done in the same vacuum chamber immediately prior to coating, as part of the same run, without any additional handling that would be prone to error or contamination. No curing is necessary. (In contrast, liquid coating processes often require many process steps with lots of part handling spread out over different locations: mixing the coating ingredients in solution or suspension; extensive pretreatment, such as heat-cleaning and grit-blasting, or ultrasonic cleaning; applying the coating material to the surface by spraying or dipping, and then finally curing the coating using heat or UV).

 

PECVD uses non-equilibrium plasma (instead of heat or chemical reactivity) to drive the reactions that create a coating, which allows heat-sensitive materials to be coated.

 

The PECVD process covalently bonds the coating to its substrate, creating strong adhesion. (Adhesion is further enhanced because the substrate was atomically clean just prior to coating.)

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PECVD typically uses these inputs:

• precursor gases or vapors volatilized from liquids (fed in from tanks)

• energy (from an RF generator)

• low pressure (using a vacuum pump)

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The PECVD process is controlled by the:

• chemistry of the plasma for a given gas(es) or vapor(s)

• flow rate of each gas or vapor

• pressure

• amount and type of energy input

• configuration of the electrodes

• configuration of the vacuum chamber inlets and outlet

• temperature of the plasma

• fixturing of the parts and their placement in the generated plasma

• special parameters of the plasma generation, such as tuning the plasma or pulsing the plasma

• amount of time that the process runs

• possible use of multiple coating steps using different precursor gases and system settings, such as to create an adhesion layer (primer) followed by a hydrophobic layer (topcoat)

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Being able to control these variables enables us to optimize the surface. We tune the plasma system to provide the desired properties for your device. Notably, PECVD enables precise control of coating thickness. PECVD coatings can be extremely thin (typically measured in nanometers, not microns or mils) and can be kept within extremely tight tolerances, as low as +/- single-digit nanometers.

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