berlin
Nanoscale Resolution Options for Optical Localization Techniques
C. Boit TU Berlin – Chair of Semiconductor Devices EUFANET Workshop on Optical Localization Techniques Toulouse, Jan 26, 2009
Nanoprobing of Identified Node se r La
● Resolution < 50nm ● Parallel lapping down to contact layer ● Isolated devices ● Low ohmic contact ● Destructive to circuit
Detector
Probe Tip
Tip
AFM Feedback
Piezo
Additonal Signals
AFP needles tungsten contacts IMD bulk-Si
PW
W NW bulk Silicon
Jan 26, 2009
EUFANET 09 Toulouse
2
Optical Backside Circuit Analysis • GHz regime managed by most dynamic techniques Laser • Feature Size Resolution: 2 levels of analysis LVP – Level 1: IR + SIL to identify critical area – Level 2: Nanoprobing to verify critical node – prep circuit destructive
CCD Photon Emission
increasing need for a high resolution optical localization technique Laser Stimulated Electrical Signal Jan 26, 2009
EUFANET 09 Toulouse
3
Trench Floor Planarity Global navigation through silicon with co-axial IR and ion column
IR-Microscope Ion Beam
DCG Systems - OptiFIB
ΔZ≈130nm
Jan 26, 2009
Co-planarity check of trench bottom to chip levels with interference rings (fringes) EUFANET 09 Toulouse
4
FIB Ultra Thin Back Surface Procedure ● mechanical thinning ● localized FIB trench - 1st endpoint on n-wells – voltage image contrast - 2nd endpoint on STI – material image contrast < 400nm remaining Si ● local high precision alignment n wells
poly p-diff actives n-diff 150µm ARC STI Jan 26, 2009
4 - 40000µm2 STI
EUFANET 09 Toulouse
5
AFP
frontside
backside
TUB Research @ ISTFA 07
● FIB backside process
● parallel lapping down to contact layer ● isolated devices ● low ohmic contact
● devices not isolated ● creation of new circuit nodes ● Circuit fully functional
● Destructive to circuit AFP needles tungsten contacts IMD bulk-Si
PW
FIB Pt W
D
S
G
NW bulk Silicon
Jan 26, 2009
EUFANET 09 Toulouse
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UltraThin Si - Ideal Platform for NanoAnalysis Ultra Thin Backside Technique
IR Technique
Visible or UV Laser Stimulation Nanoprobing, C-AFM E-Beam Techniques: - Voltage probing - E Beam induced photocurrent
LADA, Dyn. LS
e-
Light
TUB Research
LVP, TRE LADA, Dyn. LS
Nano Probes
STI
n-well ≈350nm
M1 M2 Jan 26, 2009
EUFANET 09 Toulouse
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Dual Gates: Ultra Thin Body not to scale
etc M2
M2 M1
Cu W
ILD
CoSi p-Poly p+ ≅ 20nm
≥ 100µm Jan 26, 2009
n-Poly STI STI
NW p-Poly
n+
BOX ≅0,3µm = Buried Oxide
≅1,5µm
PW n-Poly
SX SX
EUFANET 09 Toulouse
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Interaction Dimensions • 20nm Gate length Technology • UTS (SOI PD) • UTB (SOI FD / Dual Gate etc)
100nm
20nm
100nm
40nm Jan 26, 2009
nm 0 2
m n 50
40nm
EUFANET 09 Toulouse
m n 20
m n 50 9
Backside Access: Transmission of Light in Silicon Spectral Absorption in Silicon Soref et al., IEEE J. of Quant. Elec., Vol. QE-23, No.1, January 1987
104
α (cm-1)
UTS: ∼ 350nm
105
Blue Light 430nm (2.8 eV): α ∼ 350nm-1
Concentration of free electrons N [x 1018 cm-3 ]
103
40 24
10
2
10
1
UTB: 20nm
T = 300 K
6
UV? EBeam?
0.32 undoped
100 0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
Photon Energy (eV) Jan 26, 2009
EUFANET 09 Toulouse
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SNOM on UTB Resolution
Photon Emission
= f (tip geometry, working distance)
but independent of wavelength !
20nm
20nm III-V
Jan 26, 2009
Ge
EUFANET 09 Toulouse
STI STI
11
SNOM on UTB Photon Emission Laser Stimulation - transferred power? LVP - SNR?
20nm
20nm III-V
Jan 26, 2009
Ge
EUFANET 09 Toulouse
STI STI
12
SNOM on UTB Resolution = f (tip geometry, working distance)
but independent of wavelength !
20nm
20nm III-V
Jan 26, 2009
Ge
EUFANET 09 Toulouse
STI STI
13
SNOM on UTB Photon Emission LVP - SNR? Laser Stimulation - transferred power? Thermal LS when tip is scanning over STI 20nm
20nm III-V
Jan 26, 2009
Ge
EUFANET 09 Toulouse
STI STI
14
FET Delay Variation on Defined Node ● shorter wave length ● absorption depth ∼ 100nm ● optical confinement by FIB trench - waveguide -
hν
● impact only on exposed transistor ● Resolution of stimulation by confinement
Jan 26, 2009
EUFANET 09 Toulouse
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FIB Guided SNOM on UTB ● Better thermal management: ● Narrow FIB Trench to UTS ● Trench as waveguide? ● or for Fiber probing?
Adaption of Sidewalls to Fiber? 20nm
20nm III-V
Jan 26, 2009
Ge
EUFANET 09 Toulouse
STI STI
16
FIBbed SIL Solid Immersion Lens (SIL) created out of the bulk silicon material → perpendicular transition Si / air, no refraction sample surface (chip backside)
removed material
object plane
Jan 26, 2009
EUFANET 09 Toulouse
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Results Images of the SIL (r ≈ 91 µm, t ≈ 34 µm) using a laser scanning microscope at wavelength λ = 1064 nm
30µm focused on SIL
Jan 26, 2009
30µm focused on background
EUFANET 09 Toulouse
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Nanoscale Potential • Technique
TUB Research
Resolution
Potential
Comment
Optical through bulk Si (IR)
500nm
100nm (SIL)
Limited resolution
Nanoprobing
50nm
10nm
E Beam
100nm
20nm
Limited dynamics Material degradation?
Optical through ultra thin Silicon
300nm
< 100nm (SIL)
Realization complex
UV through ultra thin silicon
150nm
< 50nm
Material degradation?
Jan 26, 2009
EUFANET 09 Toulouse
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Jan 26, 2009
EUFANET 09 Toulouse
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Ultra Thin Body UTB SOI: Partially depleted = PD
VGS = 0
Poly DepleGate ted Si
Fully Depleted FD
BOX Si
|VGS| > |VT|
Conductive Channel
Subthreshold Slope ≅ 60mV / dec FD active layer ∼ 20nm => UTB Jan 26, 2009
EUFANET 09 Toulouse
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