Lee,

At low excitation frequency PECVD Silicon Nitride films tend to be
compressive.  Above a few meaghertz the ion peening effect is reduced and
the films tend to be tensile.  PECVD SiN films can be deposited with
virtually zero average stress by using dual frequency excitation.  With this
approach one alternates between low, e.g. 25-450 KHz and high, e.g. 13.56
MHz.

At low frequency the compressive stress may be reduced by running at
ralatively high pressure, however above ~2 Torr the uniformity deteriorates.

A typical process I have used is 330 sccm SiH4, 2000 sccm NH3, 2 Torr, 380
degC, 300 watts of RF power at 25-450 KHz.  The stress was ~ 6E9 dynes/cm2
compressive.  This same process could result in zero average stress with the
addition of 13.56 Mhz excitation.

If you don't have access to a dual frequency reactor let me know and I can
put you in contact with a source for these films.

Roger Shile
Shile@Endevco.com



-----Original Message-----
From: lee ki seong 
To: MEMS@ISI.EDU 
Date: Friday, September 25, 1998 7:22 PM
Subject: A. low stress Si3N4 in PECVD ?


>Hi. colleague
>
>Is any body know how we can get low stress Si3N4 in PECVD using SiH4, NH3
>   RF POWER, Temp, Pressure, Vacuum.
>
>If some body has a trend to lessen the stress, would you inform me ?
>
>with thanks.
>