WorkShop Audace INSA ROUEN 8 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
GPM: High Technology instruments Electric caracterisation of the componants life mode ageing Pulsed IV measurment unit Ageing bench in L and S band Chemical or laser depackaging Laser Sésame 1000 Laser ablation Jet Etch II Chemical opening
Default localisation : Photon Emission Microscopy Si-CCD- high sensibility camera: OBIRCH laser diode option 1300nm 90mW; Prober SussMicroteK PM8DSP PHEMOS 1000- Hamamatsu Photonics France Reactive ion etching plasma Source RF 300W 13.56MHz Plasma Concentrator Gaz: SF 6, CF 4, CHF 3, O 2, Ar Plasma Lab 80 Plus-RIE/PE
Microstructurale analyse SEM / FIB SEM-FIB NVISION 40 zeiss LDMOS cross section HR TEM JEM ARM200F JEOL FEG gun - Probe Cs corr HRTEM micrograph
APT (atom probe tomography) LAWATAP APT 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 P OUT 50W ( P3dB datasheet) Power added efficiency greater than 60% to P3dB
Electric caracterisation Ageing conditions Pulsed-RF saturated running VDS0 : V DSBR /2 IDS0 : 0mA (Classe B) Operating frequency : Band S Flange temperature : 20 C Stress 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 reliability study» by J.B. Fonder
Loss of electrical performances 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
Default localisation: Photon Emission Microscopy (PEM) - Unstressed device = quite uniform distribution of Photon emission along the 80 fingers - 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 more degradation at the centre than the edge - 3 TEM samples Fresh TEM-1 Superimposed PEM images. Bias point is VDS=20V and ID=100mA for both devices. White squares localize TEM samples. Scale bar = 100µm Aged TEM-3 TEM-2
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) HRTEM micrograph of the Ni/AlGaN interface of the stressed sample gate contact (TEM-3) Elemental composition of the TEM-3 schottky contact (EDS line scan)
Schottky contact TEM-1 Drain side AlGaN Ni Au Si 3 N 4 GaN - 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 TEM-2 Au - Temperature gradient effect Ni Si 3 N 4 Au Drain side AlGaN GaN Ni TEM-3 Au AlGaN Ni Si 3 N 4 Drain side AlGaN GaN STEM-HAADF gate contact micrographs Scale bar = 100nm GaN EDX overlay maps Au (blue) /Ni (green) /Al (red)
- Ni / nickel oxyde / AlGaN Au / nickel oxyde / AlGaN - Phenomenon linked to Vp shift and Schottky barrier drop HRTEM micrograph of the Si 3 N 4 /AlGaN passivation interface at drain side (TEM-3) Elemental composition of the TEM-3 schottky contact (EDS line scan) - No degradation of the passivation layer - No delamination of the Si 3 N 4 / AlGaN interface
Conclusion Pulsed RF-life tests degradation non-uniform Schottky contact PEM analysis = non uniform signature along the die TEM analysis = Schottky contact modification = consistent with electrical measurements Edge damage < centre damage = consistent with a temperature gradient. Temperature measurments are occuring. As part of the AUDACE project, new instruments (Depackaging, PEM, RIE) are used to study the reliability of new technologies. These new instruments, associated to the GPM equipments (SEM/FIB, TEM, ATP), strengthen GPM expertise in the field of reliability.
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