Re: Reason for cracks in PECVD silica post-annealing
Michael Larsson
2007-03-12
Hi Uday,
Aside from a multi-stage deposition process, you could try to increase
the annealing temperature. I have no practical experience with PECVD
silica, but annealing at 620 deg C may be insufficient to generate
sufficient material softening to achieve the degree of stress-relief
you require. Pure (bulk) silica normally softens at temperatures in
excess of 1500 deg C. If the layer contains diffused impurities, it
may soften at lower temperatures.
Another possibility is that the cooling process is too rapid. I am
sure you have done this, but try to cool your sample in graduated
stages. Assuming the annealing temperature is sufficient to soften
your layer and relieve internal stresses, these can quickly redevelop
during cooling because of temperature differentials that arise through
the thickness of the oxide layer. The temp gradients cause
differential thermal contraction, effectively 'locking-in' a new set
of stresses after annealing. Such an effect would generally be more
prominent with increasing layer thickness. A similar process may be
occurring at the interface between your deposited layer and the
substrate, leading to a shearing force that delaminates your film
shortly after cooling. Just a few thoughts...
Let us know how you get on.
Regards,
Michael
> Hi Everybody,
> I have been depositing 1.6 micron silicon dioxide by PECVD process
at 300 degrees temperature on silicon wafer coated with silicon nitride,after
that I am annealing at 620 degrees.Here I am having a problem that the deposited
oxide is peeling off,might be due to high stress ,so someone suggest me some
solution to sortout this problem.
>
> Thankyou and Regards,
> Uday.