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Comparison among modeling approaches for gate current
computation in advanced gate stacksARCES: N.Barin, C.Fiegna, E.Sangiorgi
BU: P.A.Childs
FMNT-CNRS: D.Brunel , C.Busseret, A.Poncet
PISA: A.Campera, G.Fiori, G.Iannaccone
POLIMI: R.Gusmeroli, C. Monzio Compagnoni, A.L.Lacaita, A.S.Spinelli
TUW: M.Karner, H.Kosina, E.Langer
UDINE: F.Driussi, P.Palestri, L.Selmi
WUT: B.Majkusiak, J.Walczak
Aim of Task 3 of SINANO Work-Package 4Study of the performance and reliability of conventional (SiO2) and
high-k thin insulator gate stacks for sub-50nm MOSFETs)
• To support the understanding of device reliability issues and potential limitations of device performance related to the gate stack architecture of future CMOS technologies.
The activities foreseen in this context are:• simulation of C/V and I/V for different gate stack and device
architectures; • investigation of the effects of high-K materials and of the related
defects, traps, charges, etc.. on the low-field mobility and carrier transport properties of the inversion channel.
Two main phases :• comparison of gate leakage currents in advanced device
architectures; • assessment of modeling requirements for ultra-thin oxide and
high-k, metal gate stacks.
OUTLINE
• Modeling approaches• Template devices• Results
– C/V– I/V– Microscopic quantities
• Comparison with experiments• Conclusions
Simulation Framework
• Solution of the Schrödinger equation in the poly-Si/dielectric/Si stack
EyV
dy
d
m )(
2 2
22poly
Diel.
Si
• Boundary conditions ?
+Poisson Equation
Boundary Conditions
Closed
In principle: no current !
Define quantum boxes
=0 at both sides of a box
Ig: semiclassical approach
Boundary Conditions
Periodical The Schrödinger equation is solved two times,applying Dirichlet and then Neumann conditions on both sides.
This is like simulating an infinite periodical structure, but only over one half period
T-prob. from the contact to the semiclassical turning point
Approaches followed by the partners
Model 1Model 2Model 3Model 4Model 5Model 6Model 7
Different definitions of the quantum boxes in closed-boundaries
OUTLINE
• Modeling approaches• Template devices• Results
– C/V– I/V– Microscopic quantities
• Comparison with experiments• Conclusions
Template Devices
• Device A: pure SiO2 (tOX=1nm) NPOLY=1020cm-3 (n-type)
NSUB=1018cm-3 (p-type)
• Device B: pure SiO2 (tOX=3nm) NPOLY=51019cm-3 (n-type) NSUB=31017cm-3 (p-type)
• Device HK: 4nm HfO2+ 1nm ITL NPOLY=1020cm-3 (n-type) NSUB=31017cm-3 (p-type)
• Device A and B are from: C. A. Richter, IEEE EDL, vol.22, p.35, 2001.
OUTLINE
• Modeling approaches• Template devices• Results
– C/V– I/V– Microscopic quantities
• Comparison with experiments• Conclusions
Results: C/V curves
•Good overall agreement•Small problems in accumulation and at beginning of inversion (different models for poly-quantization)
HK
OUTLINE
• Modeling approaches• Template devices• Results
– C/V– I/V– Microscopic quantities
• Comparison with experiments• Conclusions
Comparison with experimentsData from N.Yang et al., IEEE T-ED, vol.46, p.1464, 1999.Same physical parameters as in the template devices.
NPOLY=1020cm-3
NSUB=51017cm-3
(from C/V)
Conclusions• Unprecedented comparison effort carried out by seven
academic groups• Good agreement between results obtained using very
different models (open/closed boundaries)• Approaches based on closed boundaries, coupled with
the evaluation of the semiclassical escape-time provide a good trade-off between efficiency and precision
• Results submitted to IEEE T-ED, 2nd review step: mandatory revisions
• Comparison of Trap-Assisted-Tunneling