Reliability improvement of Atomic Force Probing on copper - eufanet

W. M1. Copper. Xbeam platinum deposition. Gate. EFA Crolles France. Ph Larré / L Brou ... CoWP coating (cobalt/tungsten/phosphorus) (75s _ PH9_75°C).
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Reliability improvement of Atomic Force Probing on copper

Ph Larré L Brou September 2008

EFA DESIGN ANALYSIS T R&D CROLLES FRANCE

Executive summary AFM Prober Generalities, equipment, working, scanning

Problematic versus analysis

Ex:Short M1M1

Difficulties on copper Oxidation Hardness

Solution Electro-less Experiments

Results

Electrical curves

Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

AFM Prober Generalities Sample SRAM cell

1700µm

4500µm

300µm

0.09µm G

Magnification x 50 000

S PMOS D

1.5µm Front-End Technology & Manufacturing

Cell

12µm EFA Crolles France

COMPANY CONFIDENTIAL

Ph Larré / L Brou

AFM Prober equipement

10mm Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

AFM Prober equipement schematic Laser Center laser on reflection photodiode level

ΔV on photodiode is driving piezo extension Photodiode

Piezo Extension

LASER DIODE

13.27

Piezo

_

Miror

+ Cantilever Tip diameter ~ 100nm

W

Schema not at scale Front-End Technology & Manufacturing

W G

Drain

EFA Crolles France COMPANY CONFIDENTIAL

Tip W

scanning diélectric

Source

Ph Larré / L Brou

AFM Prober equipement scanning Schema at scale

W dedicated equipment

W 700 µm

Tip B

Tip A

90nm

W

EFA Crolles France COMPANY CONFIDENTIAL

Dielectric

G

Drain Front-End Technology & Manufacturing

W

Source

Ph Larré / L Brou

AFM Prober equipment scanning Schema at scale

W dedicated equipment

W 700 µm

Tip B

Tip A

90nm

W

EFA Crolles France COMPANY CONFIDENTIAL

Dielectric

G

Drain Front-End Technology & Manufacturing

W

Source

Ph Larré / L Brou

Problematic

Cross section FIB/SEM of a SBF

M1 Copper

M1 Copper

Contact

Contact W

Xbeam platinum deposition

Gate

W

Contact

Contact

W

W Gate

Source

Drain

No defect at contact level

Source

Drain

Defect at M1 level Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

Problematic No defect detected by charge contrast technique

SEM charge contrast

FIB charge contrast

We need to probe on copper Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

Difficulties of M1 level Sample is quickly damage by the tip scanning

1st scanning

2nd scanning

Damages

Topo Images

Accumulation of copper at the end of the tip Reliability of the solution? Front-End Technology & Manufacturing COMPANY CONFIDENTIAL

Difficulties on copper Low hardness Immediate oxidation Elasticity depend of cristal orientation

E=60 GPa

E=180 GPa

10um

Cristal orientation

E=120 GPa

¾Extracted from: Propriété des couches minces et des interconnexions de cuivre, thèse de Magali Grégoire Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

Experiments on electro-less Cobalt coating (3 steps) : Pre-clean (cleaning solution) (30s) Palladium activation (etch + coating) (10s) CoWP coating (cobalt/tungsten/phosphorus) (75s _ PH9_75°C)

Palladium coating (2 steps) : Pre-clean (cleaning solution) (10s) Palladium coating (etch + coating) (60s)

Copper surface preparation Palladium coating (etch + coating) (60s)

Teflon precelle

Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

Solution: Electro-less Palladium (Pd) (~5 à 10nm) + + + +

Simple to implement Process well controlled Good selectivity on copper Good stability of the electro-less deposition Liquid solution

Conductive surface Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

SEM tilt view after Pd electroless

Evaluation of the process quality

Tilt 30°

etch + palladium deposition: The coating is too thin to be observed

Cell

M1 recess 1um

¾ Uniformity ¾ Good selectivity ¾ Little M1 recess

Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

AFP scanning after palladium electro-less 1 mn Topographique Image

Pico-current Image Negative bias on tip +60pA

3um

cell

cell

-40pA

Gate

Source PMOS

30nm

• Good image quality • Outline well defined (TaN/Ta) Front-End Technology & Manufacturing

• Good image quality • Good homogeneity • Stability of the image quality during few days (#5) EFA Crolles France

COMPANY CONFIDENTIAL

Ph Larré / L Brou

Electrical characterisation results at copper M1 level on a reference cell 75uA

NMOS

Vg=1.2V

pull down

Vg=1.2V Æ Idsat ≈ 75uA

Vg=0.9V

Id

Vg=0.6V 0

0

Vd

70uA

NMOS pull down

Vg=0.3V; 0V 1.2V

Vd=1.05V

Vt≈400mV

Id

Vd=0.55V

M1 level versus contact level Æ Same values

Vd=0.05V

0 0

Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

1.2V

Vg Ph Larré / L Brou

Palladium electroless solution used Product name: ENCAP ACT 2.1 Supplier: Enthone

Next step Solution for CMOS045 and CMOS032 REFERENCES 1-Grégoire M., “Propriétés des couches minces et des interconnexions de cuivre”, Thèse, Spécialité Science et Génie des Matériaux, INPG, 2006 2-R.Mulder, S.Subramanian, Tony Chrastecky, “Case Studies in Atomic ForceProbe Analysis” 3-P.Singer, “The Advantages of Capping Copper With Cobalt ”, Semiconductor International, October 2005 4-L.Peters, “45 to 32nm : Another Evolutionary Transition”, Semiconductor International, January 2007 5-B. Lee “Electroless CoWP Boosts Copper Reliability, Device Performance”, Semiconductor International, July 2004 Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou

Read state ‘1’ Vdd

Even if the channel is not active the Vdd level is going through the defect to the drain

Vdd

BLT

WL

WL

BLC

‘1’

SA

Front-End Technology & Manufacturing

EFA Crolles France COMPANY CONFIDENTIAL

Ph Larré / L Brou