90
W. C. Law and S. De W. Wong
Fig. 19 The illustration of the oxygen showering setup and etch damage recovery mechanism by the
oxygen showering post-treatment (OSP). Adapted from and reprinted with permission from J. Jeong
and T. Endoh, “Novel oxygen showering process (OSP) for extreme damage suppression of sub20 nm high density p-MTJ array without IBE treatment,” in VLSI Technology (VLSI Technology),
pp. T158-T159: IEEE (2015)
glancing incidence of 80° to reduce the lateral size of the MTJ without compromising
the aspect ratio.
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. However, the 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,
thus IBE is insignificantly slower than RIE. In addition, high beam angle etching may
cause possible edge damage on the MgO barrier, degrading the MTJ performance,
and the maximum beam angle is limited due to the shadowing of high density arrays
of MTJ structures [192].
Even though the patterning of high density MTJs for STT-MRAM products is
achievable with the current IBE manufacturing tools, the CMOS industry still heads
towards the direction of RIE processing for device patterning due to the lack of
experience and issue of beam divergence leading to wafer-to-wafer non-uniformity
in 300 mm wafers processing. Nonetheless, the ferromagnetic material such as Co, Fe,
W. C. Law and S. De W. Wong
Fig. 19 The illustration of the oxygen showering setup and etch damage recovery mechanism by the
oxygen showering post-treatment (OSP). Adapted from and reprinted with permission from J. Jeong
and T. Endoh, “Novel oxygen showering process (OSP) for extreme damage suppression of sub20 nm high density p-MTJ array without IBE treatment,” in VLSI Technology (VLSI Technology),
pp. T158-T159: IEEE (2015)
glancing incidence of 80° to reduce the lateral size of the MTJ without compromising
the aspect ratio.
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. However, the 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,
thus IBE is insignificantly slower than RIE. In addition, high beam angle etching may
cause possible edge damage on the MgO barrier, degrading the MTJ performance,
and the maximum beam angle is limited due to the shadowing of high density arrays
of MTJ structures [192].
Even though the patterning of high density MTJs for STT-MRAM products is
achievable with the current IBE manufacturing tools, the CMOS industry still heads
towards the direction of RIE processing for device patterning due to the lack of
experience and issue of beam divergence leading to wafer-to-wafer non-uniformity
in 300 mm wafers processing. Nonetheless, the ferromagnetic material such as Co, Fe,