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

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 3

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

Temp

Tm

Tr

Glass

Crystalline

Liquid

Programming history

EFUG 2008, Frans Voogt, September 29, 2008

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

EFUG 2008, Frans Voogt, September 29, 2008

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

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 6

Viewdirection

FIBetch

TEM sample preparation: FIB pluckering

EFUG 2008, Frans Voogt, September 29, 2008

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

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 8

Backside circuit-edit FIB’s

CMOS090

Enhanced etch rates withspecial gases (XeF2)

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 9

Applied to PCM cells

Navigation with IR camera

Bondpad

Bondpad

Cell

Cell can be programmed !!

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 10

From FIB to TEM in four steps

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 11

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

Charge accumulation due toimplanted Ga ions→ discharges through cell

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 12

Solution: Pt wires

Bond pads short-circuited → discharges through wire

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 13

Beam damageSample heating → diffusion → voids

Make samples as thin as possible

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 14

Single cells processed in CMOS13

“RESET” “SET”

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 15

Transfer to C065 process

CMOS13 single cell

C065

8×10 array

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 16

Different designs, same procedure

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 17

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

C13 cell

Becomes more and more of aproblem with shrinking dimensions

C065 cell

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 18

Ga haze

Not only etching, but alsoimplantation

~1 nm per 1 keV→ ~30 to 50 nm

Ga+ ions

EFUG 2008, Frans Voogt, September 29, 2008

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

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 20

Sample improvement

Shadowing

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 21

Outlook

• Further optimize oxygen sputtering

• Ph.D project RU Groningen

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 22

Also for other types of sample!

Substrate

BOX layer

SOI layer

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 23

First results SOI wafers

HAADF image: overview sample

HR BF image →(100) crystal lattice SOI film

Hole

EFUG 2008, Frans Voogt, September 29, 2008

CONFIDENTIAL 24

Acknowledgements

Romain Delhougne (PCM samples)

Harry Roberts (FIB)David Donnet

Claud van Oers (ToF-SIMS)