What is molecular vapour deposition?
Co-authors and contributors
- Dr Lee Hitchens, Nexus
- Mike Kosla, Applied Microstructures
Molecular Vapour Deposition (MVD) is a vacuum deposition process that was invented and patented by Applied Microstructures (AMST) in 2004.
The MVD process produces a highly conformal thin film coating, typically less than 100nm.
The coating provides excellent barrier properties and surface energy control. Processing cost is kept low by utilising batch processing.
What type of coatings does the molecular vapour deposition process produce?
MVD technology is used to make coatings such as:
- Electrical insulation films
- Liquid and vapor moisture barriers
- Corrosion and oxidation barriers
- Lubrication and anti-stiction films
- Hydrophobic or hydrophilic surfaces
- Biocompatible surfaces
- Reactive coatings
How does MVD actually work?
In the MVD process, small amounts of gas-phase chemicals are introduced into the process chamber and react at surfaces to form films.
Unlike traditional CVD and ALD flow systems, the MVD reaction takes place in a chamber under static pressure resulting in extremely low chemical use.
Samples are typically maintained at temperatures ranging from 30°C to 80°C during deposition.
What family is MVD from?
MVD belongs to both the families of chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods.
Where is MVD used in technology applications?
Typical applications include:
- Non-stick coatings for sophisticated microelectronics and parts found in smartphones, computers, displays, automobile sensors, and hard disks
- Non-wetting coatings used on inkjet nozzles
- Surface functionalization for biological assays
- Anti-fouling and lubrication coatings for parts implanted in the human eye
- Dielectric films used in virtual reality displays
- Release layers for nano-imprint lithography
Advantages of MVD
Quality of finish
The advantage of the MVD process over a comparable liquid phase process is the control and minimization of particulates on the treated surface.
Cost of process
MVD does appear to be a much faster process compared to Parylene to create like for like protection.
Also, it does not require silane pre-treatment and it only requires small amounts of chemicals. As a result, PCB processing cost could be very low compared to Parylene.
Complete Coverage
The MVD process is designed to produce 100% coverage of all exposed surfaces on complex parts.
Conformal coating thickness control.
The MVD process manages film thickness and thickness uniformity by dosing exact amounts of precursors and controlling reaction times.
Many other processes like Parylene are dependent upon amount of dimer and will continue to deposit successive polymer layers until it is completely used up causing thickness variation across the chamber.
Multiple laminate layers are possible
MVD allows single component layers for basic barrier protection or customized laminate layering for complex requirements.
Most other films including Parylene are single component layers.
Water vapor transmission rate (WVTR) is lower than Parylene
The WVTR < 0.1 g/m2-day for a fast deposition time and < 0.00001 g/m2-day for a longer deposition time. Parylene WVTR is typically 0.5 g/m2-day
Light transmission
MVD films are optically transparent and do not affect light transmission or reflection due to the relatively low coating thickness.
Electrical insulation
A component in the MVD coating is a flexible ceramic layer that acts to help preserve electrical isolation over time. This can give a highly insulating coating finish.
Pinhole-free
MVD films are pinhole-free at a nanometer level thickness. Parylene and some other materials are only pinhole-free at micron levels.
Coating stability. Coatings stable up to 450°C environment.
Ease-of-Use
The MVD system is fully automated and requires only a push of a button to run a process recipe.
Disadvantages of MVD
Substrate Cleanliness
This is important to the quality of finish similar to many other vapour deposition processes.
The MVD substrate cleanliness requirement is similar to that of Parylene.
MVD is a batch process
This can have a limiting factor on throughput although scaling the system is easier than a Parylene system due to the conformal nature of the coating throughout the chamber.
Process time
Standard coating deposition time is on the order of 2 to 3 hours per batch process
Deposition time depends on number of coating layers required. Process time is limited by chamber size.
Masking Requirements
The need for masking is dependent on the barrier requirements.
For ultra thin coatings masking may not be required. in other cases it may be essential.
Cost of Process
Ultimately, MVD may not be cost effective for certain levels of electronics.