Sandra,
I would not necessarily worry about diffusion through the wafer. The
more important problem is the "spiking" effect that may occur when Al
diffuses in silicon, which will affect the quality of the contact. I
think you would better off if you could raise the doping of the silicon
by other means (ion implantation/boron/phosphorus diffusion).

MIchael Pedersen
MEMS Exchange

Sandra Bermejo wrote:

> Dear Ravi,
> Thanks for your answer,
> I usually make an anneal in H2N2 ambient for 20 minutes. The temperature
> ranges from 450:C to 500:C. I wonder if I can raise this temperature avoiding
> the diffusion of aluminium trough the wafer.
> Best regards,
> Sandra
>
> Ravi Shankar ha escrito: