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DEPFET Sensor – a Status Report. L. Andricek, P.Fischer, G.Lutz, R.H.Richter, M.Schumacher, M.Trimpl, J.Ulrici, N.Wermes. DEP (leted) F (ield) E (ffect) T (ransistor) operation principles DEPFET prototype run Technology and design Wafer thinning Concept, first results.

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DEPFET Sensor – a Status Report

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Depfet sensor a status report

DEPFET Sensor – a Status Report

L. Andricek, P.Fischer, G.Lutz, R.H.Richter, M.Schumacher, M.Trimpl, J.Ulrici, N.Wermes

  • DEP(leted)F(ield)E(ffect)T(ransistor) operation principles

  • DEPFET prototype run

    • Technology and design

  • Wafer thinning

    • Concept, first results

MPI Munich (HLL) and Bonn University

Ladislav Andricek, MPI Halbleiterlabor


Depfet sensor principle of operation e g jfet

radiation

55Fe-spectrum @ 300K

single pixel

~1mm

-

-

-

+

-

+

-

+

+

-

ENC = 4.8 +/- 0.1 e-

DEPFET Sensor - Principle of operation (e.g.JFET) -

~300 mm

Advantages: Amplification of the charge at the position of collection

=> no transfer loss

Full bulk sensitivity

Non structured thin entrance window (backside)

Very low input capacitance => very low noise

Ladislav Andricek, MPI Halbleiterlabor


Depfet sensor linear mosfet for small pixel

DEPFET Sensor - linear MOSFET for small pixel -

MOS transistor instead of JFET

A pixel size of ca. 20 x 20 µm² is achievable using 3µm minimum feature size.

Ladislav Andricek, MPI Halbleiterlabor


Depfet matrix principle of operation

switch on row

&

common source readout

clear internal gate

DEPFET Matrix - Principle of operation -

Ladislav Andricek, MPI Halbleiterlabor


Depfet sensor technology development

Pre-test diodes

IBulk =100pA/cm2

-> like in old technology

DEPFET Sensor- Technology Development -

Self aligned double poly / double aluminium process

on high ohmic n- substrate

along p-channel

Ladislav Andricek, MPI Halbleiterlabor


Depfet sensor layout

DEPFET Sensor- Layout -

  • 2 pixels

  • 30 x 30 µm²

  • DEPFET

  • L = 5 µm

  • W = 18 µm

  • reduce the required read out speed by 2

    doubles the number of read out channels

Ladislav Andricek, MPI Halbleiterlabor


Depfet sensor prototyping current production status

N-side view with two polysilicon layers

and contact openings

1 Pixel cell

Drain

Gate

Still to do:

- P-side processing

- Metallization

Clear

Expected to be finished:

Spring 2003

Clear

gate

Source

DEPFET Sensor- prototyping/current production status -

Many test arrays on a 6“ Wafer

- Circular and linear DEPFETS

up to 128 x 128 pixels

minimum pixel size about 30 x 30 µm²

- variety of special test structures

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors the idea

Processing thin detectors- the Idea -

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors wafer bonding

Processing thin detectors- Wafer bonding -

10 “SOI” Wafer prepared by

MPI für Microstrukturphysik, Halle

≈1 cm/sec

picture from: www.mpi-halle.mpg.de

Q.-Y. Tong and U. Gösele “ Semiconductor Wafer Bonding ”

John Wiley & Sons, Inc.

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors anisotropic wet etching

Processing thin detectors- anisotropic wet etching -

Hydroxide etching of silicon: KOH, NaOH, … , TMAH: (CH3)4 NOH

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors first tests

Processing thin detectors- first tests -

Handle Wafer:n-type, 1-100 Ohm.cm, (100), thickness 283 - 297 micron

Top Wafer:n-type, 1-3 kOhm.cm, (100)

* BOX layer: Oxide 245 nm

* wafer bonding

* annealing for 4 hours at 1050 ºC to 900 ºC.

* grinding and polishing of device wafer (Sico)

After bonding, thinning, and polishing top layer thickness:

24 - 29 micron (3 Wafer)

36 - 38 micron (3 Wafer)

43 - 47 micron (4 Wafer)

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors first test mask koh etching at cis

Processing thin detectors - first test mask / KOH etching at CiS -

Processing at CiS (5 wafer):

*deposition of 60nm Si3N4 masking layer on SiO2

*Dry etching of the windows, open oxide layer

*KOH etching at 80 ºC

*remove nitride layer

50x13 mm2 (tesla/2, one supporting bar)

(50x13)/2 mm2 (3 supporting bars)

80x10.4 mm2 (80% of tesla sensor)

6.5x6.5 mm2

(50x13)/4 mm2 (7 supporting bars)

drawbacks of KOH etching:

1.) poor selectivity to oxide -> nitride mask

2.) poor selectivity to Al

3.) alkali ions –> not CMOS compatible

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors distortions

26 μm

51 μm

Processing thin detectors - distortions -

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors first test mask tmah etching at hll

good selectivity to oxide

almost perfect selectivity to Al

no alkali ions

poorer selectivity to (111) (≈30:1)

rough surface after etching (hillocks)

Etch solution:

5 wt.% TMAH

1.6 wt.% dissolved silicon

0.4 wt.% (NH4)2S2O8

-> at 80 ºC

forms a passivation layer on Aluminium pads:

Aluminium-oxide

Aluminium silcates

{

}

Processing thin detectors - first test mask / TMAH etching at HLL -

Tetra-Methyl-Ammonium-Hydroxide

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors tmah etching at hll results

ATLAS Pixel Detector

(Al on 500 nm SiO2)

after 10 h at 80 ºC

on ≈40 μm thick Silicon

Processing thin detectors - TMAH etching at HLL/ results -

etch rate (100): ≈35 μm/h

etch rate of Al, wet SiO2: < 1 nm!!

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors next steps status

unstructured n+ on top

structured p+ in bond region

Device Wafer

Handle Wafer

structured p+ on top

unstructured n+ in bond region

Processing thin detectors - next steps / status -

Diodes on thin silicon:

* test bondability of implanted oxide

*electrical performance of diodes on thin silicon

* process evaluation and more mechanical test

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors next steps status1

Processing thin detectors - next steps / status -

p+ diodes on top:

simplified standard technology

white areas are thinned to 50 μm after processing

p+ diodes in bond region

Ladislav Andricek, MPI Halbleiterlabor


Processing thin detectors next steps status2

Processing thin detectors - next steps / status -

Bonded wafers (structured implant in BOX):

Bonding possible, but some voids after annealing!

-> improve surface condition before bonding

infrared transmission pictures from MPI Halle (M. Reiche)

Ladislav Andricek, MPI Halbleiterlabor


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