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Defining Silanes

Q:  I've used Silane in my furnace to make polysilicon coatings for many years.  We had to handle it with great care.  Lately, I've been hearing about silanes in all kinds of applications.  Are people talking about the same thing? 

A:  First of all, what is a silane?  Chemically speaking, a silane is any silicon-containing compound.  In a semiconductor fab, silane gas (SiH4) is used in high temperature furnaces to create polysilicon films.  Silane gas is pyrophoric and may explode if it is mixed with air.  It is also highly toxic.  No wonder it has to be handled with great care! 

The silanes that are being talked about so much in research papers the last few years are not the same thing.  Actually, organosilane is a more exact term for the chemicals – that is, a compound containing a carbon to silicon bond.  In general, they are much more stable and safer to handle than the silane gas used in a semiconductor facility.  These compounds allow the user to bond to a wide variety of substrates such as glass or silicon and have an array of different functionality.

Next, we'll examine the functional groups and some of their most common applications.

1)   Creating a Hydrophobic Surface – There are many applications that require a surface to resist moisture uptake.  The semiconductor industry started using hexamethyl-disilazane (HMDS) many years ago and vapor deposition of HMDS is well established in the marketplace.   Other chemically simple Alkyl Silanes such as octyltriethoxysilane (OTS) are commonly used as well. 

2)   Creating an Anti-stiction Coating – Another major application of silanes is for anti-stiction properties.  Fluorinated compounds such as tridecafluoro-triethoxysilane (containing 13 fluorine atoms) or heptadecafluoro-triethoxysilane (containing 17 fluorine atoms) are commonly used creating a TeflonÒ-like coating.

3)   Creating a Reactive Coating – Some application require the coating to react with subsequent coatings or depositions.  There are a wide variety of silanes designed for these applications such as AminoPropylTriEthoxySilane (APTES) which leaves an amine functional group to react or 3-Glycidoxypropyltriethoxysilane which leaves an epoxy ring at the end of the chain to react other compounds.

Silane coatings are being used for everything from DNA microarrays to making fabrics stain resistant to helping adhere paint to concrete.  The organosilanes discussed here (along with many others) can be coated in vapor-phase using the YES-1224P system for the ultimate in uniform coatings.