C2 volatile

 (AsCl





 sample (GaAs)

 a) Reactive neutral species
 combine with sample surface to
 form a volatile species that
 leaves the substrate; non-
 directional etching.


 Ar or Cl
 non-volatile
 I / (GaClx)





 sample (GaAs)

b) Charged ions accelerated
toward substrate at near-normal
incidence. Removal of substrate
material or non-volatile etch
product may occur. Etching is
directional.


Figure 7. Non-directional versus directional etching.


a) Rounded sidewalls due to
increased chlorine flow. The
concentration of chlorine reactants is
increased. This increases the amount
of chemical etching which tends to be
isotropic.


 S GaC13
 GaAs
b) The accumulation of GaC13, a less
volatile species, at the bottom and
sides of the feature often result in a
loss of etch depth and feature
definition. With increased chlorine
flow and the increase in chlorine
reactant concentration, more GaC13 is
formed.


Figure 8. Etch profiles due to increased chlorine flow.

 Adding Ar into the plasma chemistry enhanced anisotropic etching. It created ion

bombardment by a non-reactive species that encouraged the volatilization of etchants

such as the often rate limiting GaC13 species. Because of this, it is expected that as the Ar

flow rate increases, the amount of ion bombardment increases, reducing the GaC13 layer