Surface activation
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Surface Activation (Surface Modification, Surface Functionalization) is the process of altering the surface energy (surface chemistry) of a material in order to favor a certain property such as hydrophobicity, reactivity, bonding, morphology, etc.
Contents
Method of operation
Plasma activation
Plasma can activate the surface by removing surface atoms thus creating 'dangling bonds" or surface reactive species. The plasma interaction can be through the chemistry of reactive species present in the plasma, such as the case of oxygen plasma, often used for cleaning surface with organic contaminants. Oxygen species react with the -C and -H present on the surface forming volatile species like H2O and CO2. Oxygen plasma is often used to activate the surface of polymers to improve adhesion, for example glass PDMS bonding. The plasma can also contain large atoms of unreactive species, like noble gasses (Ar, Ne) which energized by the plasma collide with the surface removing surface species via momentum transfer. This is often used in cases of metal surfaces which will oxidize in the presence of an oxygen plasma for example.
UV Ozone activation
UV-Ozone besides removing carbon containing materials from an inorganic solid surface, can also permanently alter the surface of polymers by removing C and H atoms inducing a cross linking of the surface. This cross-linked top layer can act as a protection layer making the polymer more resistant to chemicals and solvents, or giving it structural integrity that will prevent reflowing when exposed to higher temperatures.
Surface chemistry modification
The advantage of chemical etching is its specificity, it allows the removal or modification of only certain elements on the surface. It can be done by dipping a surface in a liquid chemical, or by exposing the surface to a gas containing the reactive chemical. Below are some examples
Wet etching
Often used to remove oxide and native from a solid this exposing the fresh surface. It is also used to expose certain faces and grain boundaries in crystalline solids. It can also be used to selectively enrich the surface of an alloy by removing the surface toms of one of the components.
Adsorption
* Adhesion promoters
This type of surface modification is done specifically to improve tadhesion on the surface, it is specific to the substances involved. For example, hexamethyldisilazane (HMDS) is widely used in the semiconductor industry to improve the adhesion of certain photoresist to the silicon surface, especially during developing and wet etching. HMDS can be applied as a liquid and spun over the surface, then when heated at temperatures higher than 110C the Si-OH surface bonds are replaced by Si-O-HMDS bonds(while releasing ammonia gas), the release of NH3 leaves allows the O on the surface to bind to the H in the HMDS molecule, making the surface hydrophobic. This process is better done in a dedicated oven, at LNF it is done in the Image Reversal Oven YES Plasma Stripper
UV Ozone activation
Chemical modification
Is done in wet benches where metals are allowed:
- Acid Bench 12
- Acid Bench 72
- Acid Bench 73
- Acid Bench 92
- Base Bench 91
- HMDS adhesion promoter application in the Image Reversal Oven YES-310TA
- PDMS release agent is applied in Solvent Bench 94
Surface morphology modification
Applications
How is this technology used in nanofabrication and what types of devices/research areas is it useful in?
- Improve hydrophobicity or hydrophilicity
- Improve adhesion
- Improve release
- Bonding
Parameters
Surface cleanliness, surface uniformity, type of material (solid, polymer, dielectric), surface energy, surface composition are all factors that affect the process of surface activation.
- To learn about surface cleaning go here: Cleaning
Materials
Surface Activation of polymers, metals, dielectrics
See also
References
- Overview [1]
Further reading
- Other stuff, e.g. technology workshop slides
- External links (can be in another section below, if appropriate)
