EXAMPLE 17: Full.Coupled Diffusion 312 SUPREM-IV.GS – 2D ...

EXAMPLE 8: Shear Stress
EXAMPLE 8 Shear Stress
DESCRIPTION
This example calculates the extent of shear stress in the silicon substrate,
generated by a film edge. It is well known that when Si 3 N 4 is deposited on
silicon by chemical vapor deposition, a large intrinsic stress is present in
the layer. If the film is continuous and sufficiently thin, this stress does not
present a problem. The substrate is much thicker (~1000 times) than the
film, so the substrate stress is 1000 times less than the film stress. If the
film is etched, however, there is a localized stress in the silicon close to the
film edge which is of the same order of magnitude as the stress in the film.
This large stress can induce dislocations directly, or indirectly through
several mechanisms. It can also induce dislocations to glide from implant-
ed regions into masked regions, causing junction leakage. Similar stress
patterns are set up by thermal expansion mismatches between the substrate
and overlying films.
A simulation of the substrate stress induced by a nitride film is shown be-
low. This example can be found in the examples/exam8 directory under
the name. A substrate is considered with mask edges aligned along
the directions. The nitride film is 0.02 m thick. The intrinsic stress
in the nitride is assumed to be 1.4 10 10 dynes/cm 2 , as reported in Irene
[1].The input deck for the simulation begins as follows.
#
# nitride on silicon example
foreach SEP ( 10 5 4 2.5 )
line x loc=( - SEP ) tag=l
line x loc=-2 spac=0.3
line x loc= 0 spac=0.1 tag=m
line x loc= 2 spac=0.3
line x loc= ( SEP ) tag=r
line y loc=0 spac=0.1 tag=si
SUPREM-IV.GS – 2D Process Simulation for Si and GaAs 277