>       Hello, everybody:
>           We are developing a microchannel etched isotropically, all I read
> about isotropic etching silicon is using HNA, with agitation, then I can get
> good circular profiles of my channel, but, my classmates told me there seems
> to be a paper about the condition about the HNA... if the mask opening size
> different, CONDITION WILL BE DIFFERENT!

Yes, this is true, the net reaction is controlled by two aspects,

1) Stoichiometry of reaction ( i.e kienetics of its chemical reaction)

2) Diffusion. (i.e. diffusion of reactants to the site and diffusion of
products away from the site.)

If your reaction rate becomes limited by the rate of the
above mentioned diffusion , then the profile of your etch will depend on
mask dimensions ( dimensions of closed/open areas), and also your profile
would be sensitive to stirring, viscosity coeffs. etc.


However  if you operate in a regime in which the reaction rate is limited
by the kinetics of the chemical reaction, ( ie. diffusion is faster by
atleast an order of magnitude than chemical kinetics) then your profile
will be absolutely mask independent, visc. indep, stirring indep. and
hence completely isotropic. This regime is easily located using the
ISO-etch curves for this particular tertiary system.

Refer to

" VLSI technology for Si and GaAs " by Sohrab Ghandhi /Wiley Eastern.

This reference has the relevant iso-ETCH curves.



>           Is that true? but I can't find any paper about it...
>           When I try etching silicon with opening (100mu m) without agitation
> by H:N:A=5:10:16 from paper, the cross section profile seems to be like cars
> two wheels, not circular...



Here your reaction is being diffusion limited , hence towards the bottom
of your pit the etchant molecules take a longer time to reach the Si
surface and therefore the etchrate is lower than the top, causing
flatness at the bottom ( compared to the top.)



>           Does anybody has experience about isotropic etching, please tell
> me, I'd appreciate it!
>
>           Thanks a lot,
>
>       Sincerely,
>                               Jerry Lee
>       Institute of Applied Mechanics
>       e-mail:iamjhlee@email.com / r6543023@gauss.iam.ntu.edu.tw
>
>
>

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Amit Shiwalkar                         Dept. Of Bio-Medical Engineering.
3,Vasant,                              IIT Bombay.
Carter Road,                           Powai, Bombay-400076
Khar,
Bombay(Mumbai)-400052
INDIA.


                     Email: amits@cc.iitb.ernet.in

" Reality Is a Figment of IMAGINATION "
                                ----------- Amit Shiwalkar

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