3D-RID The application of micro- machining to radiation imaging detectors.
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3D-RID
The application of micro-machining to radiation imaging
detectors
3D-RID Val O’Shea Como 9/10/’03
3D-RID -- a detector development project funded bythe European Commission
Partners: Applied Scintillation Technologies (UK)Czech Technical University (CZ)Metorex Oy (FI)Mid Sweden University (SE)Royal Institute of Technology (SE)Surface Technology Systems (UK)University of Freiburg (DE)University of Glasgow (UK)
3D-RID Val O’Shea Como 9/10/’03
Outline of talk:
Motivation for 3d -- what is it?
Simulation
Processing -- micromachining
Devices
Conclusion
3D-RID Val O’Shea Como 9/10/’03
3D type detectorsX-rayphoton
Legend:BC = Back contactROIC = Read out circuit
1. Scintillator 2. Scintillator 3. Neutron absorber 4. Direct pn-junctionlight guiding to CCD pn-junction detection pn -junction detection detection
pp+-+--+-++-+-
E E
n
de
pth
Si CCD
CsI
Si pitch
X-rayphoton
Si
ROIC
CsI+ -
+ -
BC
Neutrons
Si
ROIC
LiF+ -
+ -
BC
ROIC
Particles
+ -
+ -
BClow doped Si
N
N
P
PSilicon orGaAs
ROIC
BC
+ -
+ -
de
pth
pitch
3D-RID Val O’Shea Como 9/10/’03
The electrodes are cylindrical and are biased to create an electrical field that sweeps the charge carriers horizontally through the bulk. The electrons and holes are then collected at oppositely biased electrodes.
Traversing ionising radiation creates electron-hole pairs in proportion to the energy deposited in the material. The free charges then drift through the device under the influence of an applied electric field. Proposed by S.Parker et al, Nucl. Instr. And Meth. A 395 pp. 328-
343(1997).
Equal detector thickness
W2D>>W3D
Equal detector thickness
W2D>>W3D
h+
e -
+ v e+ v e -v e
x
W
ionising radiation
E
h+
e-E
-ve
+ve
n
n+
p+
-ve -ve
W2D
x2D
3D
3D
3D Geometry
3D-RID Val O’Shea Como 9/10/’03
ISE SimulationElectric Potential Distribution
50m pitch 300m thick silicon doping: 1x1019 /cm3
10 m pore diameter 50 x 90 m pitch 300 m thick silicon
3D-RID Val O’Shea Como 9/10/’03
ISE SimulationElectric field Distribution
• 50V bias
3D-RID Val O’Shea Como 9/10/’03
ISE Simulation
3D-RID Val O’Shea Como 9/10/’03
2D MEDICI software package
Si material parameters.Schottky barrier height= 0.65eV.SRH statistics +impact ionisation.No charge trapping or surface current.Sidewall damage caused by reactive ion etching, ND=1017atm./cm3.
-160 -140 -120 -100 -80 -60 -40 -20 0-1.6x10
-3
-1.4x10-3
-1.2x10-3
-1.0x10-3
-8.0x10-4
-6.0x10-4
-4.0x10-4
-2.0x10-4
0.0
MEDICI simulation MEDICI simulation with dry etching defects cathode-biased (experimental)
Cu
rren
t(A
)
Bias(V) Simulated cell Defect distribution
MediciSimulation
3D-RID Val O’Shea Como 9/10/’03
3D- Detector Structure
Unit cell
Pixel
n+
p+
50
m
50 m
35 m
p+
p+
n+
n+
35
m
50 m
3D-RID Val O’Shea Como 9/10/’03
Simulated Depletion Voltages
Si
ND [cm-3] 1012 1013 1012 1013 1012 1013
Pixel size [m]
50 50 100 100 150 150
Vdepl. [V] 1.7 15 6.5 70 20 190
3D-RID Val O’Shea Como 9/10/’03
–Connection from the readout & detector die combination to the communication / utility
circuitry
Basic image cell : vertical hybridisation of detector, read-out electronics & Interface circuitry & connector
3D-Stacked Imaging Tiles
Courtesy Eric Beyne IMEC
3D-RID Val O’Shea Como 9/10/’03
Tiling of 3D-image stacks
• Tiling on frame :
– flexible design,
– high accuracy alignment
Courtesy Eric Beyne IMEC
3D-RID Val O’Shea Como 9/10/’03
Preamp
DiscL
Double Disc logic
Vth Low
Vth High
13-bits
Shift Register
Input
Ctest
Testbit
Test Input
Maskbit
3 bits Threshold Adjust
3 bits Threshold Adjust
Shutter
Mux
Mux
ClockOut
Previous Pixel
Next Pixel
Conf
8 bits configuration
Polarity
Analog Digital
DiscH
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
195 200 205 210 215 220 225
THL DAC
Su
m o
f T
ota
l Co
un
ts
Cd109 Data
2 Peak Gaussian Fit
22KeV Gaussian Fit
24.9KeV Gaussian Fit
Charge Sharing and Photon Counting
Medipix2 Schematic
Courtesy Xavi Llopart and the Medipix Collaboration
3D-RID Val O’Shea Como 9/10/’03
Conventional ICP Source
Gas Inlet
Plasma Chamber
Ceramic Process Chamber
Process Height
Wafer/Sample
MESC CompatibleIsolation Valve
Temperature ControlledBellows Sealed Electrode
Helium CoolingGas Inlet
Weighted Clamp(Optional)
Pumping Port
13.56 MHzRF Matching Unit
~
13.56 MHzRF Matching Unit
~
3D-RID Val O’Shea Como 9/10/’03
Process Results - Si
10m diameter pore50m pitch8m thick PR mask<1% exposed area
Results: • 182µm depth• 40:1 selectivity to PR• 2.0µm/min
3D-RID Val O’Shea Como 9/10/’03
Process Results - Si
10m diameter hole50m pitch7-8m thick remant PR mask<1% exposed area
SF6 / C4F8 ProcessASE-HRM Source
3D-RID Val O’Shea Como 9/10/’03
Process Results - Advanced GaAs Etch (AGE) Process in ICP
Cl2 / SiCl4 + CH4 Switched ProcessProfile Angle =89.6°, Etch Rate = 1.25m/min, Selectivity=6.7:1,Depth = 37m
3D-RID Val O’Shea Como 9/10/’03
Process Results - GaAs
•Scallops visible in walls
•Anisotropic profile
3D-RID Val O’Shea Como 9/10/’03
TOPS:The Strathclyde Electron and Terahertz to Optical Pulse SourceStrathclyde University..
• 3mJ laser pulses.• 40fs pulse duration.• 1kHz pulse repetition rate.• 400nm wavelength.
Ti:Sapphire laser
Femtosecond laser
Cold processing.Low shockwave damage.
Tapering.Repeatability.Surface debris.
Advantages:
Disadvantages:
Laser drilling
3D-RID Val O’Shea Como 9/10/’03
diameter :•entrance hole:10m.•exit hole: 6m.
depth: 200m.
Laser drilling
3D-RID Val O’Shea Como 9/10/’03
Electrochemical Etching• Chemical reactions between Si atoms, HF solution and “h+” (positive charge carriers)
• HF concentration• Current density• Applied bias• Light intensity• Temperature• Silicon properties (type, orientation, resistivity)
Setup - ParametersP la tin u mE lec tro d e
n S i
V
I
E lectro ly te (H F so lu tio n )
h +
3D-RID Val O’Shea Como 9/10/’03
Macropore formation: Principle
• SCR (electric field) in silicon
• h+ directed towards the pore tips
Anisotropic etching
• Passivation of the pore walls is due to the SCR (Lehmann’s model)
Importance of the silicon resistivity !
• Condition for stable pore formation
J at the pore tip = Jps
Possibility to control the diameter
V
I
S C R
H F so lu tio n
3D-RID Val O’Shea Como 9/10/’03
Preprocessing for electrochemical etching
Front side: Inverted pyramids focus the current lines (h+)at the top of the pyramids
Back side: Formation of an Al grid uniform back side contact(especially for high resistivity sample)
Al
Si
Photolithography + KOH etching
Al deposition + photolithography + Al etching
3D-RID Val O’Shea Como 9/10/’03
Formation of pores by EE: Large pores
Spacing = 30-45 um; Depth = 230-260 um; Wall thickness 4 um; Active area > 80%.
S i
Electroly te
300 WH alogen Lam p
A l g rid
Pt E
lect
rode
P ow er Supp ly
IV
M eta llic ring
3D-RID Val O’Shea Como 9/10/’03
Images of the samples D32 and D41 ( = 2-5 kcm)
Demonstrators - Thindrill
Depth 200 mdia: 10-12
Depth 360 mdia: 10-16
3D-RID Val O’Shea Como 9/10/’03
Formation of pores by EE: Thindrill
I n m 1 2 3 4
Spacing 50 50 50 30
Depth 220 320 260 145
Diameter 12 18 12-20 12
1 2
3
4
3D-RID Val O’Shea Como 9/10/’03
Large pitch (45 or 30 µm) High resistivity ( = 2-5 kcm)
Depth: 380 µm, wall: 4 µm, Pitch: 30 µm, aspect
ratio 100!
Large pores - Sloped Walls
Depth: 180 µm, pitch: 30 µm, diameter from 6 to 18 µm. A linear function was applied to
the current.
i (mA
)
dep
th
2 63
3D-RID Val O’Shea Como 9/10/’03
Diffusion 1: 1150ºC, 1h45’
Profile along A
A
5 µm
AFM
SSRMThickness at the pore bottoms: 3 m.
Thickness on a planar wafer (SIMS): 6 m.
Transport of boron down to the pore bottom may be limited.
Formation of pn junctions: Results from diffusion
3D-RID Val O’Shea Como 9/10/’03
Diffusion 1: SIMS profiles at different positions along the pore depth:
- No B in the substrate (profiles c, g). Walls fully doped.
n - ty p e s u b s tra te
b o ro n d o p e d re g io n
c , g : su b s t ra te
d , i : b o tto m
e : m id d le
f , h : to p
boro
n do
ped
regi
on
0 1 2 3 4 5 61E15
1E16
1E17
1E18
1E19
1E20dei f
h
gcB
oron
con
cent
ratio
n (c
m-3)
Depth (microns)
Substrate: c g
Pore bottoms: i d
Pore middle: e
Pore tops: f h
Formation of pn junctions: Results from diffusion
3D-RID Val O’Shea Como 9/10/’03
Diffusion 2: 1050ºC, 1h10’. SIMS profiles at different positions along the depth:
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.01015
1016
1017
1018
1019
1020
Bor
on
con
cent
ratio
n (c
m-3)
Depth (microns)
Pore tops: m p
Pore middles: n o
Pore bottoms: k l
Substrate: j n - ty p e su b s tra te
j : su b s t ra te
k , l : b o tto m
n , o : m id d le
m , p : to p
b o ro n d o p e d la y e rs
- [B] in pores [B] in a planar sample; no significant variation along pore depth.
- Boron atmosphere in the pores maybe more uniform at 1050ºC than at 1150ºC.
- Boron layers on each side of the walls.
Formation of pn junctions: Results from diffusion
3D-RID Val O’Shea Como 9/10/’03
SCM at a pore bottom of a DRIE matrix after deposition: typical signature of a pn junction
SCM AFM
A
Profile along A
PN Junction Formation: Results from LPCVD
3D-RID Val O’Shea Como 9/10/’03
n - s ilico n
C s I:T l
p + s i lic o n
X - ra y
n -
CsI
:Tl
E c
E v
B u lk c o n ta c t
p + c o n ta c ts
p +
Why: concept of x-ray imaging detector below
Formation of pn junctions on walls of pores
Process steps: 1. Formation of pore arrays 2. Formation of pn junctions in pore walls
3. Filling pores with a scintillator, CsI(Tl)4. Contacts and bump-bonding to the ROC
3D-RID Val O’Shea Como 9/10/’03
Making ElectrodesMetal evaporation:
Ti (33nm)Pd (33nm)Au (150nm)
Tracks of Al (150nm)
Wire bonding (25µm wire)
3D-RID Val O’Shea Como 9/10/’03
3D GaAs Performance
241Am
Readout by DASH-E(P.Sellar – RAL)
Bias 10V
Run at –30 C as thereis no leakage currentcompensation
3D-RID Val O’Shea Como 9/10/’03
Conclusion
•Much more to do
•Si diode arrays 256X256 and 55 um pitch are being made
•Charge integrating chip for this array is designed -- Analogue Medipix
•Testing of and characterisation of bumped assemblies
•Improvement of filling uniformity – other fillings
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