ENABLEMENT OF COMPACT MODELS FOR

ENABLEMENT OF COMPACT MODELS FOR ULTRA-SCALED CMOS TECHNOLOGIES D. YAKIMETS, P. SCHUDDINCK, D. JANG, M. GARCIA BARDON, N. SHARAN, B. PARVAIS*, P. RAGHAVAN, AND A. MOCUTA IMEC, KAPELDREEF 75, 3001 LEUVEN, BELGIUM *ALSO WITH VRIJE UNIVERSITEIT BRUSSEL, BELGIUM 10 TH INTERNATIONAL MOS-AK WORKSHOP DEC. 6, 2017

log 2 (#transistors/$) LOGIC ROADMAP VIEW 20nm: First sign of trouble Double patterning (cost!) Planar device runs out of steam Less happy scaling era Still doubles but device scaling provides diminishing returns 10-7nm: More trouble Multi-patterning cost escalates 14nm: FinFET FinFET device saves the day 28nm 20nm 7-5nm: At last... EUV reduces cost 7nm 10nm 5nm DTCO 14nm Track height reduction Scaling boosters 4-3nm: Nanowire/sheet FET to 2nm: continue gate High-NA length scaling EUV? 2nm 1.5nm 3nm Heterogenous scaling 2D Material for power gating Back Side PDN MRAM. New Compute Machine learning Quantum computing Cryogenic electronics STCO Happy scaling era # transistors per area doubles every two year for same cost 90nm 65nm 40nm 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 Focus of process technology innovation is Scale device and wire Scale basic logic cells Scale (sub-)system functions 2

SCALING IS ABOUT POWER-PERFORMANCE-AREA (PPA) AND COST (C) 7nm Node CGP [nm] MP [nm] Cell height Number of fins Area 5nm 7nm 56 40 7.5T 3 1.00 5nm 48 28 6.0T 2 0.48 3nm 3nm 42 21 5.5T 2 / 1 0.29 Recent scaling trends have involved cell height reduction and fins depopulation causing FEOL structural changes (taller fins / nanosheets) Relative increase in MOL / BEOL importance 3

SCALING IS ABOUT POWER-PERFORMANCE-AREA (PPA) AND COST (C) 0.70 V 7nm 5nm 3nm What device architecture / MOL scheme can enable required massive PP gains? 0.65 V -60% -40% Which performance boosters are needed? Stressors Low-k spacers Contact improvements How to enable PPA with compact models? (TCAD is too slow to cover all experiments) 4

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA RO simulations Parasitics compact model Core compact model (calibrated to TCAD and HW) 5

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA RO simulations Parasitics compact model Accurate compact models for both intrinsic transport and RC-parasitics are crucial elements of the flow 6 Core compact model (calibrated to TCAD and HW)

OUTLINE Introduction Compact model structure: Intrinsic part Parasitics Example of RC-extraction for vertical transistor Summary 7

OUTLINE Introduction Compact model structure: Intrinsic part Parasitics Example of RC-extraction for vertical transistor Summary 8

HARDWARE-INFLUENCE ON CM DEVELOPMENT EITHER DIRECT ORTHROUGH TCAD 9

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA RO simulations Parasitics compact model Core compact model (calibrated to TCAD and HW) 10

TCAD-BASED COMPACT MODEL FOR INTRINSIC TRANSPORT EXTENDED BSIM-CMG TCAD CM Fitting based on BSIM-CMG model BSIM parameters Ballistic Ratio (Literature or advanced sims) Lg dependence 1. Current (IV) fitting: I DSAT (Lg, Stress) = I BAL (Stress)*BR(L G, Stress) U0 VSAT Ballistic current (TCAD S-band) 1. Full ballistic currents are independent of L G and V D. 2. Quasi-ballistic current by applying BR (L G, Stress) 3. CM is assumed to have no series resistance and ideal electrostatics (Turned off all related BSIM parameters) 2. Capacitance (CV) fitting 1. Capture QM charge centroid behavior 2. Decoupled from IV fitting (QMTCENCV=1) CGS(D)O CGS(D)L QM0 PQM ETAQM TOXP SS DIBL Electrostatics and charge (TCAD DD with QM-corrections) SS/DIBL 3. SS/DIBL fitting CDSC CDSCD DVT1SS CIT ETA0 DSUB DVTP0 DVTP1 11

DRIVE CURRENT BALLISTIC CURRENT Full ballistic current provide good indication of intrinsic potential of various devices Si 0.5 Ge 0.5 PFET Si NFET LNW D=7nm FF FinH 30nm, FW 5nm Vdd=0.6V, Ioff = 3.5 na May be easily simulated as a function of stress 12

DRIVE CURRENT BALLISTIC CURRENT TIMES BALLISTIC RATIO = TARGET DRIVE CURRENT Ballistic ratio is tricky to compute as various scattering mechanisms affect it Si 0.5 Ge 0.5 PFET Si NFET LNW D=7nm FF FinH 30nm, FW 5nm Vdd=0.6V, Ioff = 3.5 na I DSAT (Lg, Stress) = I BAL (Stress)*BR(L G, Stress) 13

HOW TO CAPTURE THIS IN BSIM-CMG? BRIEF THEORETICAL BACKGROUND BSIM model has been described with a drift-diffusion model which is defined by carriers mobility (μ DD ): At low fields μ DD μ low At high fields (high V DS and/or short gates) v sat defines μ DD μ DD (E) = μ low 1 + μ lowe v sat This results in two key parameters: μ low and v sat The μ low is replaced by the apparent mobility due to ballistic mobility reduction and additional scattering mechanisms. 1 = 1 + α μ μ app μ long L G 14

CAPACITANCE FITTING BOTH CHANNEL CAPACITANCE AND OVERLAP CAPACITANCE SHOULD BE FITTED FinFET Lg=30nm FW5/FH30 Nanowire Lg=30nm 7nm diameter S-device TCAD results Cgate fitting S-band (no Cov) NanoSheet Lg=30nm 5nm NSH thickness S-device w/ Density gradient TCAD (maker) Fitting results (line) 10, 15, 20nm NSH width Included bias dependency at off-state S-band on long channel ideal device Gate capacitance (channel & S/D overlap) is fitted to S-device TCAD for short-channel devices. 15

Drain current (A) HOW TO CAPTURE THIS IN BSIM-CMG? BY MODIFYING CHARGE CENTROID Confinement has been considered in CV fitting by using QMTCENCV=1 but this does not change IV results (i.e. decoupled). 8.E-05 7.E-05 6.E-05 5.E-05 4.E-05 3.E-05 2.E-05 1.E-05 0.E+00 QMTCENCV = 1 QMTCENCV = 0 0 0.2 0.4 0.6 0.8 Gate Voltage (V) <BSIM-CMG v107.0> 16

FITTING PROCESS FOR ELECTROSTATICS THE LAST STEP TOWARDS INTRINSIC COMPACT MODEL L G dependency of SS/DIBL at fixed V DD / I OFF (TCAD) <BSIM-CMG v107.0> Tuning BSIM parameters for SS/DIBL separately SPICE simulation at varied L G and same I OFF for single fin structure Comparing between CM and TCAD SS Vt roll-off DIBL Done. In v107.0 BSIM-CMG, Vt roll-off and SS were decoupled by introducing the DVT1SS parameter which simplified fitting a lot. 17

ION (ua) SUMMARY ON INTRINSIC TRANSPORT Quasi-Ballistic (S-band + Ballistic ratio) Device model (CM) Electrostatics (S-device) FEOL parasitics imec CM is calibrated with quasi-ballistic current quantum-mechanical CV 18 70 60 50 40 30 20 10 0 electrostatics based on TCAD simulation TCAD CM(Quasi-Ballistic) CM(+Electrostatic) 10 15 20 25 LG (nm)

OUTLINE Introduction Compact model structure: Intrinsic part Parasitics Example of RC-extraction for vertical transistor Summary 19

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA RO simulations Parasitics compact model Core compact model (calibrated to TCAD and HW) 20

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA RO simulations Integration-dependent, hard to maintain in the analytical form even for FF/NW/NSh. Switched to finite element modelling for the RC calculations Parasitics compact model Core compact model (calibrated to TCAD and HW) 21

FLOW FOR PPA ASSESSMENT AT IMEC QUITE COMMON FOR THE INDUSTRY Hard to construct for advanced devices (VFET/CFET, etc.) INV layout PEX deck Annotated netlist (cell parasitics + device parameters) PPA Macro-model goes hand-in-hand with device recognition in the PEX deck RO simulations Integration-dependent, hard to maintain in the analytical form even for FF/NW/NSh. Switched to finite element modelling for the RC calculations Parasitics compact model Core compact model (calibrated to TCAD and HW) 22

POSITION OF THE MACRO MODEL Device model covers parasitic components up to the self-aligned IM1 contact Enforced boundaries result in capacitance loss, say from IM2 to fins (this picture is a bit old, layer names changed, but the idea is correct) 23

DISTRIBUTED RC NETWORK COV IS MODELLED IN BSIM Various resistances: Extension S/D Epi Contact M0A core material M0A liners BSIM-CMG Capacitances are computed with 3D finite element modeling software Resistances and capacitances are connected in a distributed network 24

EDGE EFFECTS BECOME MORE AND MORE CRITICAL (DUE TO CELL HEIGHT REDUCTION AND FIN DEPOPULATION) Simplified analytic model on relaxed pitches 3D simulations critical at tighter pitches with actual designs from.gds accounting for all fringe capacitances 25

ACTUAL DESIGNS FROM.GDS BUT STILL WITH THE SAME DISTINCTION BETWEEN MACRO AND PEX Output is at M1, not captured during 3D RC extraction pmos nmos Independent simulations might be needed if devices are not symmetrical There are a lot of various devices in a full cell library heavy.va look-up tables have to be generated 26

FULL TCAD BASED DTCO THAT IS PROBABLY WAY TOO HEAVY Calibrated TCAD deck 27

YET, THE IDEA OF RC-EXTRACTION FROM A CELL ISATTRACTIVE (IN THE FORM OF DISTRIBUTED RC-NETLIST) (Almost) no need in a macro model Lighter PEX deck because of simplified device recognition No missing capacitances because there would be no macro / PEX boundary ------------- Can this be fast and to be used for full library characterization? As otherwise this solution is limited to the path-finding PPA on RO-level. 28

OUTLINE Introduction Compact model structure: Intrinsic part Parasitics Example of RC-extraction for vertical transistor Summary 29

AN EXAMPLE OF RC-ANALYSIS OF A VFET DEVICE WHY VERTICAL? --GATE PITCH BUDGETING IS CHALLENGING Spacer Gate Spacer Contact T SP L GATE T SP L SD CGP = Contacted Gate Pitch Parasitic capacitance Reliability Electrostatics control Direct S/D tunneling Gate stack Access resistance S/D stressors 30

AN EXAMPLE OF RC-ANALYSIS OF A VFET DEVICE WHY VERTICAL? --GATE PITCH BUDGETING IS CHALLENGING Parasitic capacitance Reliability Electrostatics control Direct S/D tunneling Gate stack Access resistance S/D stressors FinFET Vertical FET 31

A VARIANT OF VFET 2-TRANSISTORS PRIMITIVES Vertical devices Common bottom S/D electrode Transistors are chained by pairs This ensures that all device terminals are accessible Physical break in the active no chaining 32

A VARIANT OF VFET NAND2 BECOMES THE SMALLEST CELL, NOT INV Series connection is typically tricky with VFETs S/D top1 S/D bot S/D top1 VDD S/D bot S/D top2 VDD Gate Si sheet channel Top Bottom SiGe S/D S/D top2 Z NAND gate structurally reduces by 50% by the absence of dummies VSS 33

A VARIANT OF VFET SELF-ALIGNED GATE Gate Top Bottom D NW = 10 nm D D = 20 nm D G S Si VFET D G S D NW = 10 nm D S = 20 nm Si & Si/SiGe VFET Si sheet channel SiGe S/D Make S/D with SiGe instead of Si Possibility to create a thinner core due to different etch rate (Si vs SiGe) 34

Capacitance [af] Gate Channel KEY CAPACITANCES Electrodes are split into logical segments: overlap capacitance capacitance to via... 70 60 50 40 30 20 10 0 G-Tov G-Bov G-Top G-Bot G-SiGe Top-Bot Across the fin view G-Bot SiGe G-Tov G-SiGe G-Bov SiGe Dielectrics: HfO 2 SiCO Oxide Conductors: Cobalt Silicon SiGe 35 Along the fin view G-Top SiGe Channel SiGe Top view G-Top Top Top-Bot Bottom

SENSITIVITIES TO KEY GEOMETRICAL PARAMETERS CAPS ARE RATHER INSENSITIVE AND DOMINATED BY OVERLAP CAPACITANCE Sensitivities are given around the middle point for every parameter G-Tov G-Bov G-SiGe (bottom) G-Top G-Bot (via) Top-Bop (via) Channel (V G = 0.65 V) 36

DEVICE RESISTANCE PLUG IS USED FOR PMOS, BUT NOT FOR NMOS Top contacts 10 nm Plug Top epi 15..25 nm Bottom epi Bottom contact 37

RESISTANCE SENSITIVITIES: TOP THE WIDER THE EXTENSION, ρ THE BETTER THE RESISTANCE R C = C A pmos nmos Holes mobility is smaller than electrons mobility in SiGe pmos nmos ] 38

RESISTANCE SENSITIVITIES: BOTTOM CURRENT FLOW IS DIFFERENT FOR NMOS AND PMOS (NAND2 CELL) nmos nmos Contact Contact pmos pmos Plug Plug nmos nmos Contact Contact pmos pmos Plug Plug ] 39

Active Power [uw] RO PERFORMANCE KEY BOTTLE NECKS MAY BE IDENTIFIED 70 60 50 40 30 20 10 0 2 3 0.90 V 1 4 0.55 V 0 20 40 60 80 Frequency [GHz] L G = 15 nm, Bottom SiGe is 25 nm thick, Top SiGe is 10 nm thick Top to bottom via spacing is 7 nm VFET config ρ C [Ωcm 2 ] N SD [cm -3 ] Ext. W [nm] Cov [%] 1 1e-9 1e20 21 100 2 5e-10 1e21 21 100 3 5e-10 1e21 18 100 4 5e-10 1e21 18 10 Overlap capacitance limits performance Resistance is less of an issue due to small currents Ext. W 40

OUTLINE Introduction Compact model structure: Intrinsic part Parasitics Example of RC-extraction for vertical transistor Summary 41

SUMMARY For pre-silicon PPA analysis of advanced nodes, CMs should be very flexible and, ideally, modules based: - stress, - electrostatics, - quasi-ballistic current... Analytical macro-model is hard to maintain as more and more device options appear + various edge effects become non-negligible. Device RC.va look-up tables may be well generated with 3D TCAD tools, but this approach is not sustainable because further library characterization would require exhaustive look-up tables. RC extraction from a full cell might be too time consuming. 42