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Fabrication of Active Matrix (STEM) Detectors
Wei Chen
Silicon Detector Group
Instrumentation Division
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Contents
Our capabilities The concept of a diode
detector Planar-technology for silicon
detector processing New processes developed for
Active Matrix detectors Current status
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Our Capabilities
Class 100 cleanroom equipped with oxidation furnace, spin-coating track, mask-aligner, sputtering system.
Simulation tools, mask design tools and testing equipment.
Strip, Pad, Pixel, Drift, Stripixel and Active matrix detectors
We are the only one in the US
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Basic Concept of Diode Detector
P-type: 0.1m N-type: 3m W=(2sV/qNd)1/2
Nd=1/q =W2/(2sV)
V~100V, W~300m,
~3kcm
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Oxidation Process
Silicon Dioxide (SiO2) provides High quality insulating
barrier Impurity-diffusion barrier Passivation Gettering of impurities in Si
Dry oxygen grown oxide (32hr)
Ambient: O2 + 0.5% TCA About 0.5µm thickness
(wafer about 400µm)
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Photolithography Process
Photoresist: Positive, S1811 (Shipley) 0.5m~2.5m
Softbake: Hotplate contact or proximity Exposure: Proximity and Contact print,
ultraviolet light Developer: MF-312 (Shipley) Smallest feature: 5µm
Produces optical images in a light sensitive film (Photoresist)
Images are a reproduction of photomask
It is an integration of steps which strongly influence one another: Photoresist and application Exposure Development
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Etching Process (New challenge)
Wet etching Chemical solution Isotropic
Advantages Low cost Reliable High throughput
Disadvantages Isotropic Photoresist adhesion Non-uniformities
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Ion Implantation
Introduces dopants as ions at controlled energies
Boron: 35keV, 1x1014/cm2 (front side)
30keV, 1.2x1014/cm2 (backside) Phos.: 50keV, 4x1014/cm2 (front side)
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Deep Implantation Mask (New)
AZ4600 Shipley Positive photoresist
>5µm thickness Blocks 520keV Boron
or Phosphorus ions implantation
Boron: 2.6x1011/cm2
Phos.: 6.5x1011/cm2
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Post Implant Anneal
High temperature process repairs damage
(700ºC, 30min) Electrically activates
dopants Ambient: N2
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Metalization ProcessSputtering
Provides contacts and interconnections
Requirements– Low resistance “ohmic”
contacts– Low sheet resistance– Reliable interconnections
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Polyimide Insulation Layer Between Two Metals (New)
Spin on: 1000RPM, 10sec; 4000RPM, 30sec
Combined with photoresist lithography
Thickness of Polyimide: ~2µm
Size of opening: 10µm
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Double Aluminum (New)
Advantages of Al– Inexpensive– Ease of forming contacts– Excellent adherence to Si and
SiO2– Low bulk resistivity (2.7 -
cm)– Excellent bondability– Easy to process
Disadvantages– Spiking– Unable to sustain high
temperatures (over 450 °C) Aluminum Oxide Need Reverse Sputtering
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Plasma Clean (New)
Ambient: Ar gas Reduces the surface contamination After polyimide process After second aluminum patterning
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Current Status
Total Mask steps: 14
Total processing steps: 193
Now: at step #177 (Coating the second Al)
Remaining: Lithography for the second Al
Clean surface with plasma
Open oxide for p-n-implants Open oxide on backside for p-
implant Photoresist mask for protecting n-
region from p-implant Oxide cut for opening up anodes Al mask for covering p-region Deep p-implant Deep n-implant Post implant anneal Oxide step cut Oxide step cut on backside First metalization First metalization on backside Polyimide Second metalization