FinFET: a mature multigate MOS technology?A wideband transistor simulation and

characterization approach

J.-P. Raskin1, T.M. Chung1, D. Lederer1, A. Dixit2, N. Collaert2,

T. Rudenko3, V. Kilchytska3, D. Flandre3

Université catholique de Louvain,1Microwave and 4Microelectronics Laboratories

Place du Levant, 3, B-1348 Louvain-la-Neuve, Belgiumraskin@emic.ucl.ac.be

2IMEC, Kapeldreef, 75, B-3001 Leuven, Belgium

3ISP, Kiev

Growing interest for MuG

• Strong limitations - Short Channel Effects - appearing for Single Gate MOS below 50 nm

• Many technological difficulties to satisfy the ITRS predictions, in terms of leakage current (IOFF), supply voltage, Early voltage, DIBL, cutoff frequency, etc.

• Multiple-gate MOSFETs (MuG) are considered as serious potential candidates

Planar MuG < > Non-planar MuG

Planar MuG

• GAA: First planar DG MOS– Isotropic wet etching of BOX– good gate oxide-channel interfaces,

channel thickness controlled by highly selective wet etching

– Need: variable W/L >< GAA (W/L=1)

• Planar DG built by wafer bonding starting with SG MOS

– Gate stacks are not built at the same time (dissimetry)

– Misalignment of top and bottom gates

• Planar DG built by transfer of a thin Si film above a cavity

– Both gates are built simultaneously– Misalignment of top and bottom gates

GAA

[Colinge, SOI Conf. 90]

SON-GAA, ST-M, IEDM’03 DG, CEA-LETI, SOI Conf. 04

DG, UCL, SPIE 04

Self-aligned DG process, but no DG MOS yet

Non-planar MuG

FinFET

FinFET, Triple gate

Omega gate, Pi-GateIMEC, SSE’04

Taiwan Semicon., IEDM’02

RF analog factors of merit• Several good published articles investigated the intrinsic behavior

of MuG experimentally and through simulations: ION/IOFF, Subthreshold slope, Vth roll-off, DIBL.

• Analyses focused on RF analog performance – not limited to the channel behavior (impact of parasitics related to the 3-D structure)

Year Lmin / node

(nm)

tox (nm) gm/gds @ 5.Lmin Parasitic cap. (fF/µm)

fT (GHz)

2005 45 / 80 2.1 100 0.24 140

2006 37 / 70 1.9 100 0.24 170

2007 32 / 65 1.6 100 0.24 200

2009 25 / 50 1.4 100 0.24 280

2012 18 / 35 1.2 100 0.24 400

2015 12 / 25 1.0 100 0.24 700

ITRS

Measured MuG

FinFET from IMEC

• Gate lengths L from 10 µm down to 50 nm

• Fin width Wfin from 10 µm down to 22 nm

• Fin height Hfin from 60 to 95 nm

• Fin spacing (Sfin) from 100 to 350 nm

• Nitrided gate oxide of 2 nm EOT

• NiSi salicide

Planar DG from UCL

• SiO2 gate oxide of 30 or 6 nm

• Si film of 87 nm

• BOX = 400 nm

• L from 20 down to 1 µm

3-D Atlas simulations of SOI MOSFETs Multiple-Gate Devices in

static and dynamic regimes

Non-planar vs. planar MuG

• Single-, Double-, Triple-, and Pi-Gate MOS• L from 200 nm down to 25 nm• Hfin = 50 nm• Tsi = Wfin = 20 nm• Tox = 2 nm• Tbox = 150 nm• Channel doping = 1015 cm-3 (undoped)

V th (V) S (mV/dec) DIBL (mV/V) L

(nm)

tSi

(nm)

Vds (V)

SG DG TG PG SG DG TG PG SG DG TG PG

0.05 0.32 0.35 - - 64.0 59.9 - - 200 20

1.00 0.28 0.36 - - 65.1 59.9 - - 47 11 - -

0.05 0.28 0.37 0.40 0.40 84.9 61.1 59.8 60.7 100 20

1.00 0.16 0.35 0.38 0.38 80.5 61.1 61.3 60.6 126 16 21 21

0.05 0.20 0.37 0.40 0.40 124.5 63.8 61.8 62.8 75 20

1.00 -0.095 0.34 0.38 0.38 110.1 64.4 62.7 63.1 395 32 21 26

0.05 0.045 0.35 0.39 0.40 198.5 77.3 75.3 74.2 50 20

1.00 -0.75 0.27 0.33 0.33 282.9 81.8 78.7 77.3 837 89 63 74

0.05 - - 0.32 0.33 - - 232.5 183.9 25 20

1.00 - - -0.35 -0.32 - - 445.4 365.3 - - 700 674

Static simulation results

- Roll-off Vth , degradation of S and DIBL for SG for Lg < 100 nm Solution: Reduce Si channel thickness (Vth control), but

technological problems in terms of uniformity and increase of Rs and Rd.

- Pi-gate present slightly better results, lower SCE

- At L = 25 nm, MuG with tSi = Wfin = 20 nm show degradation of their performance

Gm/Id: efficiency to convert DC to AC

Intrinsic voltage gain = Gm/Gd = Gm/Id x Id/Gd

= Gm/Id x VEA

FinFETs Planar SOI SG and DG

Measurement results

Volume inversion (VI)

1E+10

1E+12

1E+14

1E+16

1E+18

1E+20

0.0 0.3 0.5 0.8 1.0Vgs (V)

Ele

ctr

on

co

nc

en

tra

tio

n (

cm

-3)

0

200

400

600

800

1000

1200

Mo

bil

ity

(c

m2 V

-1s

ec-1

)

SurfaceCentre

Simulation results

• Clear interest for DG for channel length < 100 nm

• VI is not efficient at high Vgo

Undoped DG and SG - - - 100 nm DG MOSFET

Early Voltage vs Wfin and L

FinFETs

Measurement results

L = 10 µm

VEA for FinFET in VI regime is 10 x higher than for FD SOI

Intrinsic analog gain

Higher intrinsic gain for FinFET of around 20 dB compared to FD SOI MOS

Dynamic analysis of MuGSimulation results

At low Vgo, the gmMuG/gmSG and CgsMuG/CgsSG ratios are > 1

At higher Vgo, no improvement on normalized gm for MuG over SG

Volume inversion in MuG only efficient at lower Vgo

Miller capacitance Cgd

Cgs/Cgd: Ratio of Control capacitance of the channel to Parasitic feedback Miller capacitance.

MuG devices achieve a higher value of Cgs/Cgd as compared to SG devices

Measured Cgs/Cgd = 3

for 60 nm FinFET

3-D parasitic capacitances

Higher parasitic capacitances: TG > DG > SG due to more complex 3-D interconnection Main part of the parasitic capacitance is related to fringing field between

gate-to-source and gate-to-drain through BOX

Normalized Cgs

Cutoff frequency

- For long L, fT of SG slightly higher due to lower parasitic C compared to MuG

- At small L, SG device, very high SCE, leading to bad fT value

- Even MuG devices with L < 40 nm, degradation appears

- To follow up the ITRS, we have to reduce Wfin or tsi as well as EOT (high-k)

Vgo = 500 mV and Vds = 1 V

FinFET: very promising technological solution at short term

Advantages: - higher technological maturity than planar DG- parasitic capacitances related to the 3-D FinFET structure are only slightly higher than for SG

Disadvantages: - reduced mobility for electrons (<110> cristalline orientation)- control of Wfin by etching + gate interface quality

- higher source/drain resistances

Conclusions – Maturity of FinFETs?

Rs, Rd → reduced gm → lower fT and fmax

Rg → reduced fmax

Short term technological challenges: gate interface quality, silicidation S/D orLow Schottky Barrier S/D contacts, integration density

Acknowledgements

• UCL clean rooms team• Mr. P. Simon for RF measurements• Dr. Jurczak Malgorzata’s group, IMEC• SINANO