Yan,

I don't think you can achieve 10A PECVD film precisely and continuously.
First few 10A are nucleation islands until they grow into a continuous
film at certain thickness, which is not precisely known. Think of PECVD as
dispensing salt on a plate from a shaker bottle (well, in principle).
Initial layer of salt is full of voids until all salt grains fill up the
voids. You don't precisely know when it will fill up most voids, but it
has high probability to be filled up at some typical thickness, assuming
uniform random distribution. A single tetrahedral Si structure takes about
2A if I remember correctly, so that means about 5 atomic layers of
tetrahedral Si structure. Very unlikely to be continous film by this
random distribution process. You need growth process in different
principle, such as fully thermal driven process or layer-by-layer chemical
process. Atomic Layer Deposition process is very precise in ultra thin
film growth, but not sure if this technique is available for Si
deposition.

Regards,
Isaac


On Sun, 25 Nov 2007, memser wrote:

> Hello all,
>      I designed an optical modulator based on a film structure. But the
requirement of precision of film deposition (PECVD, Oxford plasma system 100)
is approximately 10 A.  It means a deposition time of 1.5 second for PECVD
amorphous silicon. I don't know whether this requirment is too difficult to
achieve. Maybe subtle changes in chamber of plasma system will lead a disabled
device, although we measure the film deposition rate every time before
fabriction.
>
> Best regards!
>
> X.Yan
> memser@tom.com
>