III-Nitride 2DEG structures and HEMTs: Technology and characterization

Transcription

1 KORRIGAN III-Nitride 2DEG structures and HEMTs: Technology and characterization Fernando Calle Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM) E.T.S.I. Telecomunicación, Universidad Politécnica de Madrid, Spain

2 Contents Activities at ISOM Role in Korrigan WP2. Material characterization Strain, H contamination WP3. Basic technologies and device models Surface treatment, ohmic contacts, passivation DC and RF characterization: high temperature WP4. Reliability: parasitics failure mechanisms kink effect (high and low T) aging tests Present and future activities in III-N HEMTs

3 Activities at ISOM General Located at ETSI Telecomunicación, Universidad Politécnica Madrid 400 m 2 Clean Room (100/1000) m 2 Characterization Labs CT-ISOM is a Spanish Scientific and Technological Facility Facilities Fabrication: Characterization: Material growth + Device processing Material properties + Device performance Research activity Magnetic materials and systems Simulations of non-metallic materials Narrow Bandgap Semiconductors (IR detectors, emitters: GaAs, GaInAsN) WBS: III-Nitrides (UV detectors, UV-VIS LEDs, SAW devices, MEMS, HEMTs)

4 How a Nitride HEMT Works Field Effect Transistor: A voltage signal at the gate controls charge flow between source and drain V DS >0 V GS <V th -5 V Charge flow in response to a positive voltage on the drain A negative voltage on the gate halts current flow L. Eastman (Cornell University) and U.K. Mishra (UCSB), IEEE Spectrum, May 2002, 28

5 / HEMT basics Excellent electrical properties: High breakdown field and electron saturation velocity Operation temperature > 500ºC Wurtzite structure: noncentrosymmetric crystal strong spontaneous polarization piezoelectric polarization in strained layers N Ga c-axis, z (0001) Compression along z axis P sp P pe P sp : tensile strain (PM growth) : slight compressive strain Polarization induced sheet charges 2DEGs without modulation doping O. Ambacher, JAP 1999

6 KORRIGAN: Key Organisation for Research in Integrated Circuits in Technology To establish an independent European supply chain for manufacturing HEMT devices and MMICs 29 partners (10 Universities) financed by MoDs EPITAXY - HEMT epi wafer growth -Advanced materials -Commercial sources SUBSTRATES -Material selection : SiC, Si, Sapphire -SiC material quality -Diameter expansion 2 to 3 DEVICES -Device processing -Device modeling -Reliability evaluation -Parasitic effects MMIC -Design -Fabrication (2 runs) -Demonstrators (HPA, LNA, switches) INTEGRATION -Thermal mngt -Assembly -Packaging -System impact POLITÉCNICA Activities on III-nitrides since 1995 HEMTs since 2000 (CIDA, INDRA, ESA) expertise on processing and assessment

7 Activities at ISOM related to III-N HEMTs Epi material characterization Structural properties: AFM, XRD (roughness, dislocations, strain, etc) Electrical properties: Hall, I-V, C-V (carrier density, mobility, contamination) E-beam lithography Processing and device fabrication Masks design Surface treatment Metallizations, etching, passivation E-beam lithography 2 µm Detail of a HEMT gate by SEM Device characterization DC and RF testing Low and high temperature Reliability and failure (aging, degradation) High T, high f probe station

8 Role of ISOM in Korrigan WP 2.3 Material Characterization C-V, X-Ray diffraction, Atomic force microscopy WP 3.1 Basic technologies Metallizations, passivation WP 3.3 Device models Electrical characterization, High T characterization WP 4.1 Parasitic effects Parasitics, Kink effects WP 4.4 Failure mechanisms

9 HEMT Mask PCM (ISOM-Korrigan, 2005) Ohmic contact PCM (up) Control (down) Passivation Research Production Air bridge PCM Control Mesa etching PCM Control Gate PCM Control Feed PCM Pads PCM Control

10 Basic HEMT Processing steps Surface treatment 1: Ohmic contacts: drain and source Ti/Al/Ni/Au (20/ /30-40/ nm) 2: Mesa isolation (RIE / IBM) 3: Schottky contact: gate Pt/Ti/Au (30/5/100 nm) or Ni/Au (30/70 nm) 4: Passivation: SiN X 5 Pad deposition: Ti/Au F. Calle et al., J. Mater. Sci.: ME 14, 271 (2003) buffer buffer 2 DEG buffer 2 DEG buffer 2 DEG 2 DEG

11 Ohmic contacts: RTA Ti/Al/Ni/Au RTA buffer 2 DEG buffer 2 DEG buffer 2 DEG (Ti/Al/Ti/Au) (Ti/Al/Ni/Au) RTA oven (875ºC, 45, N 2 ) Electrical test: Ohmic contact resistance: (R ~ 0.5 Ω.mm)

12 Mesa etching buffer 2 DEG buffer 2 DEG Etched region SiCl 4 /Ar/SF 6 (10:5:2) rate = nm/min RIE system Profiler: sharp step ~200 nm high Electrical: R iso > 500 MΩ/sq

13 Gate Schottky contact Surface cleaning Source Drain treatment / etching Gate Pt/Ni/Au or Ni/Au buffer 2 DEG buffer 2 DEG Focus on: Gate - Alignment - Sharp-linear edges Source 1.3µm Drain - Cleanliness Electrical test: gate leakage current

14 Schottky contact: submicron gates Lg > 1 µm Lg < 1 µm buffer 2 DEG 2 DEG Gate Source L g = 0.3µm Drain Issues: - low R g values - T-shape technology - short channel effects

15 Surface treatment and Passivation (SiN) buffer 2 DEG buffer 2 DEG - Pre deposition: cleaning with N 2 or O 2 plasma - Deposition of SiN by PE-CVD - Alternatives: AlN, high-k oxides? Key processing step for high RF output Protects device surface Minimize trap effects M. F. Romero et al., IEEE EDL 29, 209 (2008) CVD system

16 Characterization systems DC Probe Station Karl Suss RF Probe Station Cascade-SUMMIT 9101 Network analyzer Agilent PNA N5230A RF Characterization - 45 MHz 20 GHz -V bias +/- 35 V -I bias 0.5 A

17 Main results I D (A/mm) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 KQ32Pb: A2C L G = 0.7 µm W G = 2x50 µm V GS = 1 V V GS = 1 V g m (ms/mm) KQ32Pb: A2C L G = 0.7 µm W G = 2x50 µm DC 0,2 40 0,1 0, V DS (V) V th ~ -5 V 20 V DS = 10 V V GS (V) f T, f max (GHz) KQ32Pb: A2C L G = 0.7 µm W G = 2x50 µm f T f max V GS = -3 V RF-HT chuck V DS (V) PNA limit (20 GHz) I D, max (V GS = 1 V) 0.8 A/mm g m, max (V DS = 10 V) 170 ms/mm P dis (V GS = 1 V, V DS = 10 V) 8 A/mm f T, max 30 GHz f max, max 70 GHz

18 Simulation of channel temperature Estimation of channel T ch at different ambient T amb by ANSYS: - Input data: geometry, thermal parameters and power dissipated - Main dissipation mechanism: conduction through the device substrate - Approximation: metallizations and passivation layers not included For same dissipation conditions, T ch (sapphire) > T ch (Si) > T ch (SiC) T channel (ºC) SiC ºC ºC 150ºC 8 100ºC 50 V DS = 16 V 50ºC ºC 0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 I D (A/mm) L G = 0.25 µm W G = 2x50 µm f T (GHz) P dis =2.7 T amb =250ºC T ch 300ºC SiC: at f T max, T ch T amb 50ºC for all T under study low self-heating But for high power, even with SiC, T ch T amb may be > 200ºC

19 Systems for HT measurements (1) LF-HT Probe Station (Jmicro) - Devices on TO-5 or TO-7, SMA conn. - Temperature range: RT 650 K - Vacuum or N 2 atmosphere - Frequency range: DC 2 GHz - Fast heating and thermal stabilization RF-HT Probe Station (Wenesco) - Devices on chuck in air atmosphere - Temperature range: RT 600 K Thermal chuck up to 800 K - Frequency range: 45 MHz 20 GHz - DC: V bias +/- 35 V I bias 0.5 A

20 Systems for HT measurements (2) Micro Manipulated LT-HT Probe System (Janis) - He closed-cycle refrigerator - Temperature range: 10 K 650 K - Temperature controller: + 2 Si diodes for LT + 1 thermocouple for HT - Sample chamber with 6 ports: + 3 LF probe stations (coaxial) 1 µm ( ) tungsten tips + 2 MW probe stations (SMA) BeCu tips: K Tungsten tips: K + 1 UV-visible fiber probe (SMA) - Vacuum up to torr - Vibration isolation table

21 DC characterization: I D & g m vs T amb I D and g m decrease and modify profile as T amb increases for all HEMTs reduction in 2DEG mobility (phonon scattering) In general, reversible behaviour at all temperatures of the thermal cycle Example: HEMT on Si with L G = 2 µm and L DS = 9 µm I DSS (A/mm) 0,45 0,40 0,35 0,30 0,25 0,20 0,15 HEMT on Si(111) g m (ms/mm) RT 50ºC 100ºC 150ºC 200ºC 250ºC 300ºC 350ºC 0,10 0,05 0,00 L G = 2 µm W G = 150 µm L DG = L GS = 3.5 µm V DS (V) V GS = 0 V 20 V L G = 2 µm W G = 150 µm DS = 4 V L DG = L GS = 3.5 µm V GS (V) Reduction of I D,max (RT to 350ºC) to 33% Reduction of g m,max (RT to 350ºC) to 31% R. Cuerdo et al., J. Mater. Sci.: ME 19, 189 (2008); IEEE EDL 30, 808 (2009)

22 RF characterization: f T, G T, G P V DS = 16 V Decrease of the threshold frequency (f T ) with T. f T (GHz) ºC ºC ºC 150ºC ºC L 4 250ºC G = 0.25 µm W G = 2x50 µm I D (A/mm) Decrease of transduction (G T ) and power (G P ) gains with T. -G P lower values related to the rise of the input and output impedances R. Cuerdo et al., WOCSDICE (May 2010) 20 G T, G p (db) A degradation can be observed after the thermal cycle. G T G p f T L G = 0.25 µm W G = 4x100 µm 24 V GS = -5 V 22 V DS = 20 V f = 2.5 GHz T amb (K) f T (GHz)

23 Measurements under pulsed bias I D (A/mm) 0,6 0,5 0,4 0,3 0,2 Period=100 µs V DD =(0:0.5:20 V) V GS =0V R=100 Ω T amb =300 K T amb =500 K 0,1 Sapphire 0, V DS (V) Pulse width: 600 ns 1 µs 5 µs 10 µs 50 µs DC Determination of T(channel) as a function of dissipated power experiment simulation (ANSYS) S. Martín et al., WOCSDICE (May 2010) Observation of self-heating effects, i.e., the increase of the channel temperature over the ambient temperature. T channel (K) Sapphire P (W/mm) Simulated 300 K 400 K 500 K Estimated 300 K 400 K 500 K

24 Failure mechanisms and reliability tests S.L. Delage and C. Dua, Microelectronics Reliability 43 (2003) Structural measurements: wafer bowing, roughness, strain, etc. Electrical measurements DC reverse measurements (leakage I G, I D ) Electrical and thermal stress tests, aging tests

25 Conditions: - Storage temperature: 350ºC ( 1200ºC) - Real time: 2000 h ( h) Aging tests AEC / (Gate=Mo/Au) AEC / (Gate=Ni/Au) AEC-1303 FAT-FET T1 (Unstressed) T3 (350ºC-2000h) AEC-1262 FAT-FET unstressed 350ºC h Current (A) Current (A) Gate: Mo/Au Voltage (V) Gate: Ni/Au Voltage (V) After thermal storage, I G decreases (>2 orders of magnitude) After thermal storage, I G increases (~1 order of magnitude) M.F. Romero et al., unpublished

26 DC performance: kink effect I D -V DS curves show some kink effect: - Step like behaviour in I D for V GS < 0 V - Maximum ~100ºC for T 200ºC - Disappears at RF under illumination Related to the presence of traps I D (A/mm) SiC RT V GS = 0 V V GS = 1 V ºC ºC V DS (V) Low T may also reveal the kink effect - due to traps created during processing Low T may also help to identify intrinsic performance of the devices R. Cuerdo et al., IEEE EDL 30, 209 (2009)

27 Strain issues Intensity (a.u.) Before ( & ) R AlN = 0,9725 R -- = 0,92 R = 1 x = 30 % t = 28 nm R = 0 After ( & ) R AlN = 0,961 R -- = 1,05 R = 1? x = 30 % t = 15 nm R = 0-1 u xx (%) Converse piezoelectric effect u zz (%) u xx (%) u zz (%) θ/2θ Anlge (º) Thickness (nm) Thickness (nm) XRD patterns show that the strain of the layers is modified by the ohmic contact deposition and annealing, as well as by the SiN passivation. F. González-Posada et al., APL 95, (2009) The converse piezoelectric effect induces changes in the strain by the electric fields in / HEMTs. Strain relaxation by CPE is only expected in the on-state operation. C. Rivera et al., APL 94, (2009)

28 After Korrigan: for communications MANGA: Manufacturable : SiC substrates and epiwafer manufacturable chain Development of the European industrial capability for high quality SiC substrates and HEMT epiwafers to establish compatibility with existing GaAs MMIC foundries and secure acceptable costs for HEMT and MMICs. 3.5 years, France, Germany, UK, Italy ( 15 M ) EoI K2: Korrigan Follow-up First meeting for expressions of interest: Brussels, Evaluation and feedback from MoDs ? France (6), Germany (3), UK (3), Italy (5), Spain (2), Sweden (2), NL (1)

29 Remaining improvements High frequency high K dielectrics, AlN L G <100 nm High temperature refractory electrodes heat evacuation (e.g., diamond) High power Normally off devices fluorination gate recess under-gate dielectrics Reduce R ON Si doping of barrier InN contacts drain recess Increase drain current increase gate width In 0.17 Al 0.83 N barrier is LM to Improved reliability due to low mechanical stress Increase h B to reduce the gate length WBG thickness ratio for higher frequency Higher spontaneous polarisation to increase the 2D gas density Material, technology, high T

30 More activities related to III-N RF power transistors (Wireless base stations) High frequency MMICs (Wireless Broadband) MEMS (Pressure sensors) Illumination (White-blue-UV LEDs) Switches (Display panels) UV-X detectors (Bio / Space) Engine Electronics (Temperature Sensors) Blue Laser diodes (Storage/Comms) Energy conversion (Automotive-aerospace) Hydrogen generation (Fuel cells)

31 Colleagues at ISOM - Prof. Elías Muñoz (IP) - Dr. C. Rivera, Dr. F. González-Posada - strain - Dr. A. Braña, Dra. A. Jiménez, D. López, M. Sabido processing - F. Romero, R. Cuerdo, S. Martín, E. Sillero reliability, high T Collaborations with - CIDA, Spain M. Verdú, F.J. Sánchez - UAM, Spain A. Redondo, R. Gago, C. Palacios - INDRA, Spain - Y. Fernández, P.P.Cubilla - III-V Lab, France - M.A. Poison - Qnetiq, UK - M. Uren - Selex, Italy - A. Cetronio - U. Padova, Italy - G. Meneghesso, E Zanoni - CRHEA-CNRS, France - Y Cordier - MIT, USA T. Palacios - UCSB, USA - Y. Pei, U. Mishra Support by - EDA and Spanish MoD through European KORRIGAN project - Spanish Ministery of Science MINANI project (TEC /MIC) Acknowledgements