WorkShop Audace

INSA ROUEN8 juin 2012

Groupe de Physique des Matériaux

Failure analysis of the HEMT GaN

Cécile Genevois

8 juin 2012

AGENDA

� Context

� GPM presentation

� GPM: High Technology instruments

� Power amplifier HEMT – GaN reliability: HPA application

� Conclusion

Context

� Control of the reliability

• Economic and Scientific issues

� Challenge of failure analysis

• Identification and highlighting of the physical mechanisms

responsible to electrical damage

� High Technology instruments

• Multiscale investigations

From macroscopic to atomic scale

GPM presentation

140 persons

8 teams

� Physic of materials

• Various materials

• Material environments

• Microstructures and properties

evolutions

• Physical mechanism studies

• APT instrumentation

� Electronic

• Electronic reliability and failure

� Electric caracterisation of the componants – lifemode ageing

� Chemical or laser depackaging

GPM: High Technology instruments

Pulsed IV measurment unitAgeing bench in L and S band

Laser Sésame 1000 Laser ablation

Jet Etch II Chemical opening

� Default localisation : Photon Emission Microscopy

� Reactive ion etching plasma

Si-CCD- high sensibility camera:OBIRCH laser diode option 1300nm 90mW; Prober SussMicroteK PM8DSP

PHEMOS 1000-Hamamatsu Photonics France

Plasma Lab 80 Plus-RIE/PE

Source RF 300W 13.56MHzPlasma ConcentratorGaz: SF6, CF4, CHF3, O2, Ar

� Microstructurale analyse

• SEM / FIB

• HR TEM

SEM-FIB NVISION 40 zeiss LDMOS cross section

JEM ARM200F JEOLFEG gun - Probe Cs corr

HRTEM micrograph

• APT (atom probe tomography)

LAWATAPAPT analyse of a bipolar transistor(acknowledgements for S.Duguay; E. Cadel

STMicroelectronics collaboration)

Power amplificator HEMT-GaN : HPA applications

� Technology choice

• HEMT GaN transistor in AB/B class

• Band S

• POUT 50W (≈ P3dB datasheet)

• Power added efficiency greater than 60% to P3dB

� Electric caracterisation

• Ageing conditions

Pulsed-RF saturated runningVDS0 : ≈ VDSBR/2IDS0 : 0mA (Classe B) Operating frequency : Band SFlange temperature : 20°CStress test duration : 700 H

Compared deep class-AB and class-B ageing on AlGaN/GaN HEMT in S-Band

Pulsed-RF Operating Life

See « Accelerating ageing tests in pulsed-RF mode: Application to power AlGaN/GaN HEMTs reliabilitystudy » by J.B. Fonder

∆ Output power (Pout): ↓10%∆ Average drain current (Ids): ↓ 4%∆ Power Added Efficiency (PAE): ↓6%∆ Average gate current (Igs): ↑150%∆ RdsOn: ↑ 8%

- Vp <0 - Schottky barrier height ↓0.1eV

=> 2 mechanisms- One reversible induced by trapped charges- One irreversible induced by physical degradations

• Loss of electrical performances

� Default localisation: Photon Emission Microscopy(PEM)

Fresh

Aged

TEM-3 TEM-2

TEM-1

Superimposed PEM images. Bias point isVDS=20V and ID=100mA for both devices.White squares localize TEM samples.Scale bar = 100µm

- Unstressed device = quite uniform distribution of Photon emission along the 80fingers

- Stressed device = ↑ light intensity at the centre= almost no photon emission at the periphery

→Non uniform degradation → non uniform drain current distribution

→ Vp more negative at the centre than the edge + ≠ temperatures → moredegradation at the centre than the edge

- 3 TEM samples

� TEM Caracterisation

• Gate structure

TEM micrograph of the gate region on TEM-3 sample. Drain=left side

Elemental composition of the TEM-1 schottky contact (EDS line scan)

Elemental composition of the TEM-3 schottky contact (EDS line scan)

HRTEM micrograph of the Ni/AlGaN interfaceof the stressed sample gate contact (TEM-3)

GaN

AlGaN

Ni

Au

EDX overlay mapsAu (blue) /Ni (green) /Al (red)

TEM-3

Drain side

Au

Ni

GaNAlGaN

Si3N4

TEM-2

Drain side

Au

Ni

GaNAlGaN

Si3N4

TEM-1

Drain side

Au

Ni

GaNAlGaN

Si3N4

STEM-HAADF gate contact micrographsScale bar = 100nm

• Schottky contact- Ni layer not uniform on the drain side = process

- ↑ stress => ↑ Ni layer alteration

- Ni layer alteration = Ni/Au interface corrugated+ Ni dissolution in several areas

- Temperature gradient effect

HRTEM micrograph of the Si 3N4/AlGaN passivation interface at drain side (TEM-3)

Elemental composition of the TEM-3 schottky contact (EDS line scan)

- Ni / nickel oxyde / AlGaN → Au / nickeloxyde / AlGaN

- Phenomenon linked to Vp shift and Schottkybarrier drop

- No degradation of the passivation layer

- No delamination of the Si3N4 / AlGaNinterface

Conclusion

• Pulsed RF-life tests → non-uniform Schottky contactdegradation

• PEM analysis = non uniform signature along the die

• TEM analysis = Schottky contact modification = consistentwith electrical measurements

• Edge damage < centre damage = consistent with atemperature gradient. Temperature measurments areoccuring.

• As part of the AUDACE project, new instruments(Depackaging, PEM, RIE) are used to study the reliability ofnew technologies. These new instruments, associated to theGPM equipments (SEM/FIB, TEM, ATP), strengthen GPMexpertise in the field of reliability.

THANK FOR YOUR ATTENTION