Spin Transfer Torque Magnetoresistive Random Access Memory
85
Fig. 16 Illustration of
reactive ion etching system
Plasma
Electrode 2
Enchant
Gas
Substrate
S 2 > S 1
Electrode 1
R
F
6.5.2 Ion Beam Etching (IBE)
Ion beam etching (IBE) is the physical etching process whereby the ions of an
inert gas (Ar, Kr, Xe) are accelerated from a wide ion beam source into the surface
of a substrate to etch away all materials to a desired depth or under layer. Since the
accelerated ions will etch all materials, it is challenging to obtain an appropriate noneroding hard mask. Typical etch rates for ion milling by Ar
+ are ~20 nm/min for SiO 2 ,
Si and photoresist, and 20–100 nm/min for metals. Therefore, IBE is insignificantly
slower than RIE. The biggest advantage of IBE is the ability of the sample stage to tilt
and rotation, and hence a sidewall cleaning at high IBE angle can be added after the
main etch to remove any re-deposited materials. The primary Ar angular beam can be
split into its vertical components, which serve as the main etching mechanism, while
the horizontal components provide a cleaning effect counteracting the re-deposition
rate [192].
The ion beam source is an Ar ion source with a radio frequency plasma generator
connected to an antenna, as shown in Fig. 17. A 1.8 MHz oscillating current in
the antenna produces an electromagnetic field, from which primary electrons obtain
energy and are agitated. The main plasma is initiated by inelastic collisions between
hot electrons and the inert (Ar, Kr, Xe) gas atoms, producing ions and electrons pairs.
Ar Inlet
Plasma
Substrate
Tilt & Rotation
Optically Aligned Grids
Mechanical Shutter
Secondary Ion Mass
Spectrometer
e
-
e
-
e
-
e
-
+
+
+
+
Plasma Bridge
Neutralizer
Antenna
Fig. 17 Illustration of ion beam etching system
85
Fig. 16 Illustration of
reactive ion etching system
Plasma
Electrode 2
Enchant
Gas
Substrate
S 2 > S 1
Electrode 1
R
F
6.5.2 Ion Beam Etching (IBE)
Ion beam etching (IBE) is the physical etching process whereby the ions of an
inert gas (Ar, Kr, Xe) are accelerated from a wide ion beam source into the surface
of a substrate to etch away all materials to a desired depth or under layer. Since the
accelerated ions will etch all materials, it is challenging to obtain an appropriate noneroding hard mask. Typical etch rates for ion milling by Ar
+ are ~20 nm/min for SiO 2 ,
Si and photoresist, and 20–100 nm/min for metals. Therefore, IBE is insignificantly
slower than RIE. The biggest advantage of IBE is the ability of the sample stage to tilt
and rotation, and hence a sidewall cleaning at high IBE angle can be added after the
main etch to remove any re-deposited materials. The primary Ar angular beam can be
split into its vertical components, which serve as the main etching mechanism, while
the horizontal components provide a cleaning effect counteracting the re-deposition
rate [192].
The ion beam source is an Ar ion source with a radio frequency plasma generator
connected to an antenna, as shown in Fig. 17. A 1.8 MHz oscillating current in
the antenna produces an electromagnetic field, from which primary electrons obtain
energy and are agitated. The main plasma is initiated by inelastic collisions between
hot electrons and the inert (Ar, Kr, Xe) gas atoms, producing ions and electrons pairs.
Ar Inlet
Plasma
Substrate
Tilt & Rotation
Optically Aligned Grids
Mechanical Shutter
Secondary Ion Mass
Spectrometer
e
-
e
-
e
-
e
-
+
+
+
+
Plasma Bridge
Neutralizer
Antenna
Fig. 17 Illustration of ion beam etching system