Practical input from the developer of vacuum vapor prime and Silylation in the
80's.  HMDS has very active NH ending to the molecule which is looking for
hydrogen, given hydrogen it quickly forms ammonia NH3, usually from water or
hydroxyl ions. When reacting with a totally dry silicon dioxide surface it
reacts with the hydroxyl ions and leaves a mono layer.  In This mono layer the
molecule is now Silicon with 3 methyl atoms. A inorganic/organic molecule, a
perfect adhesion for  an organic photoresist to adhere to an inorganic substrate
Silicon. Bill Moffat

Sent from my iPad

On Dec 16, 2013, at 5:44 AM, "Gianmario Scotti" 
wrote:

> Hello Sk,
>
>
> I am no HMDS expert, and am talking from memory, so don't take my word for
> any of this:
>
>
> 1: Yes, I believe HMDS is polar, just by looking at the molecule.
> 2. and 3: HMDS forms a monolayer on SiO2, glass and hopefully (some)
> metals, making the surface hydrophobic. Since we're talking of monolayers,
> the thickness is probably below 1 nm. During sylilation by HMDS, some
> ammonia may be produced.
>
> You will find more info in this reference: F. Deyhimi, J. A. Coles, Helv.
> Chim. Acta 65, 1752 (1982)
> Rapid Silylation of a Glass Surface: Choice of Reagent and Effect of
> Experimental Parameters on Hydrophobicity
> http://onlinelibrary.wiley.com/doi/10.1002/hlca.19820650610/abstract
>
>
>
>
>
>
>
> On Thu, Nov 21, 2013 at 8:17 PM, Sk Fahad Chowdhury <
> [email protected]> wrote:
>
>> Hi
>>
>> I have a few questions about hexamethyldisilazane or HMDS
>> (CH3-Si-NH2-Si-CH3)
>>
>> 1.       1. Is HMDS a polar molecule? Is there any dipole present?
>> electronegativity values of constituents are : H 2.2, C 2.55, Si 1.9, N
>> 3.04. Carbon (2.55) - flourine (4) bonds are polar because of their
>> electronegativity difference.
>>
>> 2.       2. How thick can HMDS on top of SiO2-Si be when it is dried in air
>> from a liquid state? Can the thickness of HMDS be determined when it is air
>> dried?
>> 3. If HMDS is air dried and some molecules are left in sample, is it going
>> to be HMDS molecule or it will be something else? Will it release ammonia?
>> Also will it be a continuous layer or there will be clustering?
>>
>> Thanks a lot :)
>>
>> regards
>>
>> Sk
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>
>
> --
> Gianmario Scotti
>
> Researcher
> Aalto University, Dept. of Materials Science and Engineering
> http://materials.aalto.fi/en/
>
> Micronova, Tietotie 3
> 02150 Espoo
> Finland
> _______________________________________________
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