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Performance Trade-Off Scenarios for GAA Nanosheet FETs Considering Inner-spacers and Epi-induced Stress: Understanding & Mitigating Process Risks
Circuit delay and RO frequency estimation methodology
RO performance comparison and design space study
Self-heating performance comparison
Conclusion
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Outline
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Motivation
Reduced stress control with introduced inner spacers
-2000
-1500
-1000
-500
0
500
1000
Top
Middle
Bottom
Str
ess
alo
ng
ch
an
nel (M
Pa)
Air-gap
horiz.
Top wire
Middle wire
Bottom wire
Air-
gap
vert.
Air-
gap
lateral
Air-gap
hor.+
vert+
lateral
(1nm)
Ref:no
air-
gap
Channel stress at end of process
Verti
cal
Cross-section
The ‘vertical’ interface is the most critical to maintain channel stress: stress is lost completely when epi from neighboring gates doesn’t join properly
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Introduction
SD
With Inner Spacer
SD
WithoutInner Spacer
W ISP W/O ISP
Stress engineering No Yes
Parasitic cap. Low High
Parasitic res. High Low
Self-heating High Low
Considered cases for electrical performance comparison▪ Option I: With inner spacer and 100 % stress▪ Option II: With inner spacer and 0 % stress▪ Option III: Without inner spacer and 100 % stress
𝜿 = 𝟕. 𝟓 𝜿 = 𝟏𝟏. 𝟗
TCAD Deck Calibration
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NMOS: Width = 11 nm, Str: 100 %
Without With
Vths (V) 0.188 0.180
Ion-lin (uA) 15.96 16.45
Ion-sat (uA) 46.3 49.2
SS (mV/dec) 75.5 71.05
DIBL (mV/V) 35.3 30.7
PMOS: Width = 11 nm; Str = 100 %
Without With
Vths (V) -0.185 -0.178
Ion-lin (uA) 19.6 18.64
Ion-sat (uA) 54.8 55.4
SS (mV/dec) 68.8 65.98
DIBL (mV/V) 29.23 40
DOPING CONCENTRATION PROFILE
Parameters NMOS PMOS
L (nm) 15 15
TNS (nm) 11 11
HNS (nm) 5 5
Spacer (nm) 5 5
100 % Stress (GPa)
0.7 -1.7
NSD (𝐜𝐦−𝟑) 1e21 1e21
NSD ext (𝐜𝐦−𝟑) 1e17 1e17
Nchannel (𝐜𝐦−𝟑) 1e15 1e15
w/ ISP w/o ISP
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ISP removal decreases NMOS on-current
𝑲𝒐𝒖𝒕 = 4𝑲𝒊𝒏 = 7.5
Stress = 0 GPa
NMOS PMOS
Vd = 0.7 V Vd = -0.7 V
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ISP Removal increases carrier scattering
45 𝝁A
64 𝝁A
40 𝝁A
68 𝝁A
𝑲𝒐𝒖𝒕 = 4𝑲𝒊𝒏 = 7.5
Stress = 0 GPa
w/o ISPw ISP
Scattering: Carrier-carrier and carrier-ion
Without scattering
With scattering
x
x
Methodology to estimate RO performance using device parasitcs