Qing--
Here's some etch-rate data. Do a search on this site and see my on-line
papers for details.

STS ASE DRIE (inductively coupled), mechanical chuck, typical HF
straight-wall recipe at 600 W
Single-crystal Si =1500 nm/min, annealed LTO = 7.5 nm/min, silicon-rich
LPCVD nitride = 21 nm/min

STS ASE DRIE (inductively coupled), electrostatic chuck, typical HF
straight-wall recipe at 600 W
Single-crystal Si =2400 nm/min, thermal oxide = 24 nm/min

STS ASE DRIE (inductively coupled), mechanical chuck typical LF
(stop-on-oxide) straight-wall recipe at 600 W
Single-crystal Si = 2400 nm/min, annealed LTO = 3.6 nm/min, silicon-rich
LPCVD nitride = 26 nm/min

Lam 480 (parallel-plate), SF6+He, 250 W
Undoped polysilicon = 920 nm/min, annealed LTO = 28 nm/min, silicon-rich
LPCVD nitride = 210 nm/min

Key points:

1. The STS DRIE recipes are far more selective at etching Si over oxide and
nitride, with oxide etching the slowest.
This has been attributed to the lower ion-bombardment energy in the
inductively coupled plasma (controlled by the platen power) than in the
parallel-plate configuration. The bombardment energy is large enough to
assist in etching silicon, but not oxide or nitride).

2. From the data in the papers, it is seen that in most cases annealing has
little effect on the plasm-etch rates of oxides,
but has a dramatic effect on their wet-etch rates in HF solutions.

----- Original Message -----
From: "Marc Straub" 
To: "General MEMS discussion" 
Sent: Sunday, April 04, 2004 6:37 PM
Subject: RE: [mems-talk] SF6 isotropic etch


> Does anyone have actual etch rate data for various recipes?
> I don't have numbers available right now, but my past
> experience using the ASE process in STS etchers is that
> nitride and Si etch at essentially the same rate, while any
> oxide is much much slower.  In fairness, the nitride films
> in my experiments were always pretty thin, and I never tried
> very hard to calculate an exact etch rate for them.  My
> point however is that nitride is not a good stopping layer,
> nor will exposed nitride features survive very well, in an
> SF6 silicon etch.
>
> BTW- the rate of oxides is highly dependent on the
> densification, so CVD oxide etches faster than thermal oxide
> for example.
>
> Hope these comments help...
>
> Marc Straub
> Solidus Technologies, Inc.
> Colorado Springs, CO  USA
>
>
> -----Original Message-----
> From: Brent Garber [mailto:[email protected]]
> Sent: Friday, April 02, 2004 2:59 PM
> To: General MEMS discussion
> Subject: Re: [mems-talk] SF6 isotropic etch
>
>
> Yao,
>
> The Si02 and Si3N4 will etch much, much, slower than the Si
> in SF6, but uit will
> etch them all.
>
> Brent
>
> Qing Yao wrote:
>
> > Hi,
> >
> > I need to do SF6 isotropic dry etch of single crystal Si.
> I was wondering if
> > Silicon Nitride and Silicon Dioxide will also be etched in
> this process. If
> > so, does SF6 has good selectivity to them? I heard that
> people can use
> > Silicon Nitride or Silicon Dioxide as mask in BOSCH
> process (DRIE). So I
> > guess SF6 does have good selectivity to them. But I am not
> sure. Please let
> > me know if you have any information about this. Thanks!
> >
> > Best Regards,
> >
> > Qing Yao
> > ___________________
> > M&IE @ UIUC
> >
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