Mitigation of Intrinsic Vt Variation using Oxygen Inserted (OI) Silicon
Channel
Suman Datta
Jeff Smith1, Hideki Takeuchi2, Robert Stephenson2, Yi-Ann Chen2 Robert J. Mears2
1University of Notre Dame, IN, USA; 2Atomera Inc., Los Gatos, CA, USA
Outline
• Variation Mitigation Techniques– 3D Techniques
• Alternate doping scheme• Effective width increase
– Planar Techniques• Super steep retrograde doping profile
• VT Variation Improvement with Oxygen Inserted (OI) Channel
• Mobility Enhancement with Oxygen Inserted (OI) Channel• Future Outlook
2
Vt Fluctuation
• Vt fluctuation is considered a fundamental technology scaling roadmap.
Punch-through Stopper (PTS) Implant
• Punch-through Stop (PTS) implants are required to suppress sub-fin leakage in sub-22nm FinFETs.
• Lower channel doping to improve carrier transport.[1] S. Natarajan et al., IEDM Tech Dig. pp. 71, 2014 [2] C. Auth et al., to appear in IEDM Tech Dig., 2017
6e20
-1e19
1e12
Net Dop. Conc[cm-3]
Active Fin Channel
Sub-Fin leakage path
Junction Depth
Punch-through Stop Implants
Effective Gate Width
Reversal of Intrinsic Variation Trend
Tri-gate was primarily intended for electrostaticsIt uses 3D factor to scale effective width to mitigate variation and reduce standard cell foootprint
Oxygen Incorporated (OI) Channel by Atomerafor Improved Intrinsic Vt Variation
Oxygen Incorporated (OI) Channel
OI Silicon Channel for TED Blocking
• Transient enhanced diffusion (TED) causes Boron/Phosphorus to diffuse upward toward surface during annealing
• OI layer blocks TED and allows targeting of lower surface concentration to improve RDF-induced VT variation.
• [3] H. Takeuchi et al., “Punch-Through Stop Doping Profile Control via Interstitial Trapping by Oxygen-Insertion Silicon Channel”,JEDS-2017
PTS Optimization with OI silicon
• Punch through stopper (PST) dopant profile optimization using OI silicon:– S/D profile (SD1: baseline )– PST profile (PST2: OI Si ) 9
AA’
BB’
OI OI
OI
FinFET Avt : RDF only
• Considering only RDF fluctuation, OI Si FinFETshows 30% improvement in σV,Th-RDF and Avt (RDF)over baseline FinFET
10
10 20 300
10
20
30
40 PTS1+SD1: Baseline PTS2+SD1: MST PTS2+SD2: Optimized
Avt3 = 0.48 mV-µm
Avt2 = 0.50 mV-µm
σ V,Th
-RDF
[mV]
1/√(LW) [µm-1]
Avt1 = 0.69 mV-µm
OI
OI Silicon channel for Mobility Enhancement
High-K Dielectric
• Oxygen Insertion creates pseudo-energy barrier in Si MOSFET channel that:– 1. Splits Δ-2 valley sub-band levels, further lowering transport effective mass.– 2. Results in electron mobility improvement over a control Silicon MOSFET
• [4] N. Xu et al., “MOSFET Performance and Scalability Enhancement by Insertion of Oxygen Layers,” IEDM 2012, pp. 127 [5] N. Xu et al., “Electron mobility enhancement in (100) oxygen-inserted silicon channel ,“ APL 107, 123502 (2015)
Dash: OI Si Channel Solid: Control Si
Distance From MOS Interface (nm)
Mobility Improvement with OI Channel with Poly Si-SiON
High-K Dielectric
• 25% electron mobility improvement (ns = 8x1012 cm-2) is observed with OI channel and SiON/Poly gate stack.
• Is this OI-induced mobility enhancement retained with HfO2/TiN gate stack?
• [4] N. Xu et al., “Electron mobility enhancement in (100) oxygen-inserted silicon channel ,“ APL 107, 123502 (2015)
SiON/Poly-Si
25%
T. J. King (Berkeley)
High-k / metal gate FETs with OI Si channel
Substrate SSLIN (mV/dec) VT,LIN (mV) ID,LIN (µA/µm) VG-VT =1V
ID,SAT (µA/µm) VG-VT =1V
OI Channel 186 854 1.94 5.05
Control 112 962 1.69 4.38
• OI channel FET shows 15% higher ID,LIN and ID,SAT over Control FET at matched overdrive.
0 1 210-10
10-9
10-8
10-7
10-6
10-5
I D (A/µm
)
VG (V)
186 mV/dec
LG = 20 µmVDS = 0.2, 1V
OI Channel Control Si
0 1 210-10
10-9
10-8
10-7
10-6
10-5
I D (A/µm
)
VG (V)
112 mV/dec
LG = 20 µmVDS = 0.2, 1V
Output Characteristics
5nm HfO2
• At fixed VG – VT , OI channel shows 15% higher ID,SAT than Control Si.
0.0 0.5 1.0 1.50
2
4
6
8
10
I D (µΑ
/µm
)VDS (V)
VGS,STEP=0.2VVGS-VT =-0.4 to 1.6V
LG = 20µm
Control Si
0.0 0.5 1.0 1.50
2
4
6
8
10I D (
µΑ/µ
m)
VDS (V)
OI Channel
LG = 20µm
VGS-VT =-0.4 to 1.6VVGS,STEP=0.2V
2 4 6 8 10100
150
200
250
300
µ n (cm
2 /Vs)
nS (x 1012 cm-2)
OI Channel Control Si
0 1 2 30
2
4
6
8
VDS = 1V
OI Channel Control SiG M,
SAT (
µS/µm
)
VGS (V)
LG = 20µm
GM and Electron Mobility
• At matched NINV = 5x 1012 cm-2 , OI channel device shows 15% higher transconductance and electron mobility over Control Si.
15%
𝜇𝜇𝑛𝑛 =𝐿𝐿𝑊𝑊
𝐼𝐼𝐷𝐷𝑞𝑞𝑛𝑛𝑆𝑆𝑉𝑉𝐷𝐷𝑆𝑆
15%
-0.5 0.0 0.5 1.0 1.5 2.001245679
10 OI Channel Control Si
N INV (
x1012
cm
-2)
VG-VT (V)-0.5 0.0 0.5 1.0 1.5 2.0
0.0
0.2
0.4
0.6
0.8
1.0
f = 1MHZ
OI Channel Control Si
C INV (
µF/c
m2 )
VG-VT (V)
Split-CV Characterization
• OI Channel shows 5.6% lower NINV at fixed VG – VT .
10nm HfO2
ΔN/NContro
l = 5.6%
Future Outlook
– Oxygen Inserted (OI) Silicon channel provides a CMOS-compatible method to simultaneously reduce VT variation and improve transistor drive currents.
– 30% improvement in Vt variation potentially with OI channel in FinFET configuration
– In both SiON/Poly-Si and HfO2/TiN gate stack, Oxygen Inserted (OI) Silicon channel provides 15% low field electron mobility enhancement.
– Future work to focus on BTI benefit of OI channel in high-k/metal gate planar FETs
Thank You
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Statistical Mobility Analysis
5nm HfO2
5nm HfO2
• Mean electron mobility is 14% higher in OI Channel FETs than Control Si FETs.
• Indicative that mobility gain is expected with OI layer with scaled HK/MG stack.
Substrate Mean µn(cm2/Vs)
σ(µn) (cm2/Vs)
OI Channel 194 16
Control Si 170 26
50
100
150
200
250
µ n @ n
S = 5
x1012
cm-2 (c
m2 /V
s)
OI Channel Control Si
