hi all,

This may help you...I did tests to optimise the RIE and plasma etching  of
silicon nitride.

About SIN plasma Etching, here is the optimum recipe I reached - of course
it is optimized for the machine I used -  :)

RF power : 200W
pressure : 225 mTorr
Flow ratio Sf6/O2 : 2/3  (I aggre SF6 is better than CF4 with   contaminate
the chamber)
SF6 flow : 10 Sccm
O2 flow : 15 sccm

here are the measurements:
SIN Etch rate :about 220nm/min
Uniformity :5%
Selectivity SIN/PR : 0.8
Selectivity SIN/Si : 1/3

About SIN plasma etching. In our setting it was more complicated as
sputtering also occurs :
A mask for SIN etch is chromium which in turn is to be patterned by
sputtering using Molybdenum as a hard mask. Finally Molybdenum can be plasma
etched (with photoresist as a mask).
If you choose this option let me know, you may encounter many problems...

good luck.

Ziyad ELALAMY
VLSI LAB, Concordia University, Montreal.
email :[email protected]

>From: Allan Hui 
>Reply-To: Allan Hui , [email protected]
>To: [email protected]
>Subject: Re: Nitride deposit and etching
>Date: Sun, 14 Jan 2001 11:18:23 -0800 (PST)
>
>Chang-Hwan,
>
>As with any process recommendations, remember to perform some test samples
>before doing the actual processing on the real samples.  I will attempt to
>answer your questions below.  Contact me directly if you have any followup
>questions so the forum is not cluttered.
>
>On Tue, 9 Jan 2001, Chang-Hwan Choi wrote:
>
> > I want to deposit Silicon Nitride layer on Si
> > substrate which has been already covered with Silicon
> > Oxide layer in some part. After that, I will do
> > plasma-etching the Nitride in some part for the next
> > wet etching step of Si Oxide and Si substrate.
>
>What's the thicknesses of the oxide or nitride layer?
>
> > The equipment for me to use for deposition and etching
> > is Plasma Therm PECVD. For etching, I will use
> > photoresist as a mask.
> >
> > For those processes, I have some questions as follows.
> >
> > 1. Is RCA Cleanning needed before nitride depostion?
>
>Depends on what you have done after the oxide deposition.  If you have
>done nothing, it's not necessary.  If you have done lithography or
>metallization somewhere, sure, RCA1 (hydrogen peroxide, ammonia hydroxide,
>DI) is good.  Keep in mind though that RCA1 may etch some metals.
>
> > 2. Which gases, what temperature(power) and pressure
> > are needed for Nitride PECVD? In that condition, what
> > is the depostion rate?
>
>Depends on how well quality you want it.  A lot of developed recipes are
>propreitary.
>For plasmatherm PECVD, there are many generic recipe's, you could probably
>contact them for one.
>
> >
> > 3. Which thickness of Nitride layer is enough as a
> > mask for Si Oxide and Si substrate etching?
>
>Dry etch? If so, will you be needing the Nitride afterward?  CF4/O2
>RIE etches both nitride and oxide (and PR too).  YOu want to make sure
>your nitride mask is > than oxide thickness.  >> if oxide is thermal
>oxide since RIE etches thermal oxide slower.
>
> > 4. Is the potoresist OK as a mask for plasma etching
> > of Nitirde?
>I don't know if you have access to an RIE.  I hope you're not using the
>PECVD to do your etching.
>If you use SF6 RIE, PR is a very good mask.  If you use CF4/O2, no.  What
>nice about etching nitride on oxide with SF6 is that SF6 stops nicely on
>oxide.
>
> > 5. Which gases, what temperature(power) and pressure
> > are needed for Nitride Plasma etching? In that
> > condition, what is the etching rate?
> >
>Again, I'd recommend SF6 RIE.  If you have access to it, let me know and I
>can give you a general recipe.
>
> > I have referred to many references, but I have no
> > experience of Nitride deposition and etching. So, I
> > hope to some advices from you all.
> >
> > Thank you.
> >
> >
> >
> > =====
> > Chang-Hwan Choi
> > Brown University, Box D
> > Division of Engineering, 182 Hope Street
> > Providence, RI 02912, U.S.A.
> >
> > Tel: (401)867-6017(H), (401)863-2656(O), Fax: (401)863-9028
> > Email: [email protected], [email protected]
> >
> > __________________________________________________
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>
>

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