fib of the beaten path - imecefug.imec.be/efug2008_03_voogt.pdf · fib of the beaten path: tem...

FIB of the beaten path:TEM plan-view analysis using circuit-edit tools

Frans Voogt

EFUG 2008 meetingSeptember 29, 2008

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 2

Roadmap

• Phase-change memories

• TEM X-section preparation

• Development of plan-view preparation method

• Associated problems:

Charging damage

Beam damage

Ga haze


CONFIDENTIAL 3

Chalcogenides: SbTe alloy (with dopants)Switching between two phases

Temp

Tm

Tr

Glass

Crystalline

Liquid

Programming history


CONFIDENTIAL 4

Use as memory cells:

Amorphous = high R → “0”Crystalline = low R → “1”

Attractive candidate for non-volatile memories (RAM):+ Much faster than Flash+ Low operating voltage+ Better data retention+ Robust against radiation

But also:- Heat sensitive


CONFIDENTIAL 5

NXP line cell concept©

Active part of the cell

• Ohmic heating of thin line• Integration in BEOL of

standard CMOS process

M1

M2

PCM cellElectrode

Transistor


CONFIDENTIAL 6

Viewdirection

FIBetch

TEM sample preparation: FIB pluckering


CONFIDENTIAL 7

From X-section to plan-view

“Double thinning”

- Time consuming- Risky: ~50% succes rate

due to stress in backend

90°

Thick cross-section

Thin plan-view


CONFIDENTIAL 8

Backside circuit-edit FIB’s

CMOS090

Enhanced etch rates withspecial gases (XeF2)


CONFIDENTIAL 9

Applied to PCM cells

Navigation with IR camera

Bondpad

Bondpad

Cell

Cell can be programmed !!


CONFIDENTIAL 10

From FIB to TEM in four steps


CONFIDENTIAL 11

Charging damagePCM lines either amorphous,with voids or blown-up altogether...

Charge accumulation due toimplanted Ga ions→ discharges through cell


CONFIDENTIAL 12

Solution: Pt wires

Bond pads short-circuited → discharges through wire


CONFIDENTIAL 13

Beam damageSample heating → diffusion → voids

Make samples as thin as possible


CONFIDENTIAL 14

Single cells processed in CMOS13

“RESET” “SET”


CONFIDENTIAL 15

Transfer to C065 process

CMOS13 single cell

C065

8×10 array


CONFIDENTIAL 16

Different designs, same procedure


CONFIDENTIAL 17

However: new problems arise...Image blurred by tiny particles...

C13 cell

Becomes more and more of aproblem with shrinking dimensions

C065 cell


CONFIDENTIAL 18

Ga haze

Not only etching, but alsoimplantation

~1 nm per 1 keV→ ~30 to 50 nm

Ga+ ions


CONFIDENTIAL 19

Solution: further sputtering with oxygen

With the aid of acalibrated ToF-SIMS tool

* Removal of Ga* Thinner sample→ Improved contrast

Low-keV O+ ions


CONFIDENTIAL 20

Sample improvement

Shadowing


CONFIDENTIAL 21

Outlook

• Further optimize oxygen sputtering

• Ph.D project RU Groningen


CONFIDENTIAL 22

Also for other types of sample!

Substrate

BOX layer

SOI layer


CONFIDENTIAL 23

First results SOI wafers

HAADF image: overview sample

HR BF image →(100) crystal lattice SOI film

Hole


CONFIDENTIAL 24

Acknowledgements

Romain Delhougne (PCM samples)

Harry Roberts (FIB)David Donnet

Claud van Oers (ToF-SIMS)

fib of the beaten path - imecefug.imec.be/efug2008_03_voogt.pdf · fib of the beaten path: tem...

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